The World God Only Knows/Shout-Out

Organized in the order of appearance. Citation(s) would be appreciated.

In The Manga

 * During the Serious Business meeting of the inner Keima's Congress to prioritize what kind of game is considered a galge game, games that have the theme of capturing girls and an ending. The debate went on and on, one Keima asked "What about a scrolling shooting game with girls?". Hmm, how many of those do we have? More than one but he is probably referring to that game
 * So the collars will explode if one of the partners dies, huh...
 * Dokuro Skull asks for Billy's Bootcamp DVD as a souvenir. (chapter 1, p.3)
 * Keima, the ultimate Strategist with god-like tendencies. (chapter 1, p.12 & p.14)
 * Keima's outfit has got to be a shout-out to Austin Powers. Wonder if he has bad teeth?
 * Multi and Saber are two of the 2D girls Keima mentions while ranting about girls in real-life. (chapter 1, p.13)
 * When Keima states that he's the "God of the Game World" (chapter 1, p.14), the image he uses is based on the 19th century painting of Jupiter and Thetis by Jean Auguste Dominique Ingres.
 * The classmates' laughter and the Art Shift involved is a shout-out to Peanuts. (chapter 2, p.5)
 * BMW - Imouto metaphor. Specific model featured is a E63 model 6-series. (chapter 2, p.13)
 * In the top-left panel, Elsie is singing "lun lun, lululu, lun lun (ルンルン　ルルル　ルンルン)". It's the opening phrase of the anime song for "The Story of Perrine". Hear it for yourself. (chapter 2, p.20)
 * Keima is playing a galge in the middle of class as usual, but if you pay attention to the text that comes out of his headphones, you'll notice he's playing School Days. (Chapter 3, p.2)
 * The two girls shown on the top panel are Elchi Cargo (middle) and Rag Urao (right) from Combat Mecha Xabungle. (chapter 4, p.13)
 * A Zaku head, an interstellar locomotive, and lastly a pumpkin carriage for our Tsunderella. (chapter 4, p.13-14 & chapter 5, p.2-3)
 * The cover of chapter 6 is an allusion to Edward Burne-Jones' painting, The Golden Stairs. (chapter 6, p.1)
 * Elsie singing "My, my, kare is (わたしのカレーは)" is a pun/allusion to Asaoka Megumi's song, "Watashi no Kare wa Hidarikiki (私の彼は左利き)". Here, "kare" is a homophone that can either be the informal Japanese pronoun "boyfriend" or "curry" in Japanese. (chapter 6, p.2)
 * Dying(?) from Capturing God Mode, Keima states "This is a blood-stained road after all... (所詮血塗られた道...)". This line is from Kushana in Nausicaa of the Valley of the Wind. (chapter 6, p.11)
 * Fujisaki Shiori, Saber, Kohaku, Hoshii Miki & Miura Azusa to name a few of the girls on the last page of Keima's dream. Here is the full version. (chapter 6, p.16)
 * The former singer/idol wife of Ken Akamatsu (of Love Hina fame) is named Kanon (Chapter 7-present)
 * Keima's uniform, the Roman salute and D-pad flags to promote The Game Idol's Era. (chapter 7, p.4)
 * The final comment in chapter 9: "is Kanon's real identity alien, time traveler or slider?" (chapter 9, p.18)
 * Invisible Kanon's descent is a shout-out to Ghost in the Shell. (chapter 10, p.3)
 * Doraemon, Suzumiya Haruhi, and Maetel are the characters on the background. (chapter 11, p.4)
 * Elsie is magically speed-growing some hell strawberries with an umbrella. (chapter 11, p.13)
 * Keima sings "Let It Be!!" with a piano out of nowhere. (chapter 12, p.9)
 * Kodama-sensei (in drill instructor uniform): "What's wrong...... That Billy guy [Billy Blanks] can run 20 laps more...." (chapter 12, p.10)
 * Elsie's drawing is a reference to the arrival of Commodore Matthew Perry's four Black Ships on July 14, 1853 at Uraga Harbor in Kanagawa Prefecture, Japan. (chapter 13, p.3)
 * The text on Keima's right, "上喜撰 / たった四杯で / 夜も眠れず", is an excerpt from a famous kyoka. The "jōkisen" here is read the same as "steam-powered ships" and shihai can also mean "four vessels". Thus, the reference. (chapter 13, p.3)
 * The ad "○ki hatsuratsu!! (○気ハツラツ!!)" is a direct parody of Oronamin C's slogan/ad, with the initial spokesperson of the campaign Kon Omura. (chapter 13, p.12)
 * "I'm telling you Lucky Star—" "Oh be quiet—" (chapter 15, p.2)
 * Keima-Black Jack with reverse seams. (chapter 15, p.9)
 * Elsie with drills. (chapter 16, p.7)
 * The three delinquents from Seikesshou Albatross. On a side note, it's a manga series, also by Tamiki Wakaki, making it a Mythology Gag as well. (chapter 18, p.7)
 * Sasuke is a Japanese soft drink introduced in 1984. Not to be confused with some emo ninja. (chapter 20, p.4)
 * Keima-Pikachu is both cute and strong. (chapter 21, p.9)
 * In the bottom-left of the fifth panel, cameos of Yukiko Mamiya and Noriko Momoi from Esper Mami can be seen. (chapter 23, p.4)
 * Keima's explanation of escaped spirits uses Boos to represent the spirits. (chapter 24, p.4)
 * "Ac-chan&middot;&middot;&middot;!! Please take Minami to the Koshien Stadium&middot;&middot;&middot;!!" (chapter 24, p.9)
 * The escaped spirit looks like a certain boss (chapter 24, p.18)
 * Keima is seen dragging a cross on his back. (chapter 27, p.2)
 * Katsuragi art shifts into 10th century Buddhist Monk Kuya Shonin. (chapter 28, p.4)
 * To the number of escaped spirits left on earth, Keima complains: "With a task like this, normally, you only need about 7 pieces. Imagine 60,000 D-gonballs!!" (chapter 28, p.5)
 * Keima-Snoopy refuses to capture a certain target. (chapter 28, p.13)
 * Keima is transformed into a cockroach, and he quotes The Metamorphosis. (chapter 29, p.12)
 * RUN! IT'S KEIMA-ZILLA! (chapter 30, p.9)
 * Keima explains the power of analyzing situations with a bit of Bullet Hell. (chapter 30, p.14)
 * The enclosed octagons on Chihiro's umbrella form the pattern of the Absolute Terror Field. (chapter 32, p.10)
 * The Axis 3D is intercepted by Londo Bell 2D girls in the third panel. (chapter 33, p.10)
 * "Beyond The Time" as BGM, please.
 * The inverted logo of Dreamcast on Keima's mask. (chapter 33, p.16)
 * "As usual, this mart feels like zombies are going to haunt—" (chapter 34, p.8)
 * The name of the mart contains the word "INAZUMA", the alternate name for Satou Shouji, the artist for Highschool of the Dead.
 * Captain Bright from the original Gundam series, working as a galge developer. (chapter 35, p.14)
 * The person Jun admires is Jumbo Tsuruma, taken from the real Japanese wrestler Jumbo Tsuruta. (chapter 36, p.4)
 * Keima is imitating Sherlock Holmes' manner of speech and "Elsea-kun" is a reference to Dr. John Watson. (chapter 37, p.3)
 * The explanation of the relationship between teacher and student, illustrated with the arcade game Donkey Kong. (chapter 37, p.11)
 * The hell bureaucracy had that... board-like thing. (chapter 42, p.2)
 * They even had an inverted iPod in the meeting. (chapter 42, p.3)
 * Keima-Adam with the broom. (chapter 42, p.6)
 * Chihiro references Riki Takeuchi in her conversation. This doesn't appear in the scanlation. (chapter 42, p.8)
 * Chihiro-Nana sings the song she wrote about the "bittersweet feeling of love". (chapter 42, p.9)
 * "No," says Keima-Shinnosuke. (chapter 43, p.12)
 * Keima, who is in withdrawal after Tsukiyo laughs at Yokkyun, is facing a familiar mecha with LCL in the background. (chapter 43, p.13)
 * Shinku, is that you? (chapter 44, p.11)
 * In the non-bonus 4-koma, Tsukiyo comments that she might be able to take a milk bath with her shrunken size, to which Keima responds, "Who are you, Shizuka-chan?" (chapter 45, p.6)
 * The title of this strip is also "Being Small is Convenient".
 * "A board game...? Your pastimes are on par with Sunset on Third Street." (chapter 47, p.6)
 * A certain bowling ball next to Haqua. (chapter 48, p.1)
 * Ayane as one of the Miss Fan's Healthy Tai-Chi instructors. (chapter 48, p.3)
 * Arale Norimaki's Angel Wings Hat, with the letters replaced, alongside Yukie calling Hakua "Hac-chan". (chapter 48, p.4)
 * Keima as Shigeo Takahashi from the Japanese comedy duo Savanna (サバンナ). (chapter 48, p.8)
 * The two-piece cross pendant from one of Honda Keiko's works on the last panel. Confirmed. (chapter 49, p.11)
 * Minami's Annoying Younger Sibling using Kamen Rider Zolda's belt and gun. (chapter 52, p.5)
 * Wait a minute, that isn't "Revolver"... (chapter 54, p.1)
 * A poster of a girl playing bass, with the letters "[Kei]on! ([けい]おん!)" visible on the bottom. (chapter 54, p.2)
 * In the second panel, Giant appears to illustrate just how bad the girls' music is. (chapter 54, p.4)
 * After pulling names from a tissue box, Ayumi accuses Chihiro of cheating, which Chihiro rejects with a face like Kaiji's. This is a reference to Kaiji in the Tissue Box Raffle, where he did cheat in the game. (chapter 54, p.5)
 * The four girls on a crosswalk? It's from the cover album of Abbey Road. (chapter 54, p.6)
 * The girls try to start a light music club. Where'd they get the idea? From watching K-On!, of course. (chapter 54, p.7)
 * Kodama also mentions that he cannot recognize such groups as the Card-Battling Club or the Voice Actor Studies Club. (chapter 54, p.8)
 * Also for Sengoku Basara in the scene where they get permission for the club. (chapter 55, p.16)
 * Keima-Mario and 1UP (chapter 57, p.4)
 * TOYOTA - Osananajimi metaphor. (chapter 57, p.14)
 * "Drive Your Dreams." is one of Toyota Motor Corporation's slogans.
 * The specific model is the one-off 2000GT roadster built specifically for You Only Live Twice (the 2000GT is only available to the public in coupe form).
 * Keima's explanation of what a childhood friend is suppose to be like. Anyone's who's played the first Tokimeki Memorial will know that that's the basic setup for main heroine and childhood friend Fujisaki Shiori.
 * What do you give to a woman with no lover? The F4! (chapter 59, p.12)
 * Where's Keima? Oh, there you are! Hmm? What's with that red-and-white striped shirt and that bobble hat? (chapter 61, p.5)
 * A shoutout to the cover of the Summer Wars light novel. (chapter 66, p.1)
 * The picture on one of the bowls Katsuragi Denma crafted... (chapter 66, p.7)
 * "You can say it's quiet, but... the countryside is its people. Without the people, traditions also die out.... It's like cleaning up the charred remains of a mansion, burnt down at the end of a serial killer streak, by a stranger who took advantage of the dispute between the head and branch families, or was set ablaze on a whim by someone like a resident with a strong dialect, or eventually someone like a suspicious shinto priest and a miko... Who'll clean it up?" (chapter 66, p.11)
 * "Those are traditions?"
 * Keima's somniloquy: "Another ending... The party got wiped out." (chapter 66, p.15)
 * The front cover of vol. 8 is an allusion to Raphael's painting, The School of Athens. Observe the pattern of the vault on the background of the painting and cover. Also, the three Keimas represent Plato (pointing upwards), Aristotle (palm facing the ground), and Heraclitus (head leaning on the hand).
 * An elder with 100+40 years of experience in ramen teaches a stranger (Elsie) how to properly appreciate a bowl of ramen... Then, it's revealed that Elsie was actually reading it off a ramen guide, just like in the movie "Tampopo". (chapter 69, p.2)
 * A mere coincidence that Sumire is the name of a flower, like Tampopo? I think not. Also, how the  changes to its owner's later on. (chapter 72, p.3)
 * The logo of Chinese restaurant Hanamura (ハマムラ) parodied in the fourth panel. (chapter 69, p.10)
 * The pig face is common in Black Jack (chapter 71, p.3)
 * Plea~sed to~ meet you~ I am a Voltorb (chapter 71, p.4)
 * Tenri's western clothing is from the schoolteacher Clara Clayton in Back To The Future III. (chapter 73, p.1)
 * Tenri and Nora as Hammer Brothers Sisters, Airi as Lakitu, and Sumire as Blooper on Keima's illustration. Additionally, the Arkanoid reference on the same page. (chapter 73, p.3)
 * I'm pretty sure this robot is a shout out to some manga (chapter 73, p.6)
 * How Keima walks in on Hakua is a parody of a scene from SHUFFLE!. Here's the anime verson. (chapter 73, p.8)
 * Manaka Takane of Love Plus. Judging from the screen, it appears the PFP has a built-in microphone. (chapter 74, p.17)
 * I though that was Kobayakawa Rinko.
 * The initial part of the imagination sequence is a reference to Heidi (chapter 75, p.7)
 * In a political debate at the United States Capitol, "YES WE CAN" is written on the lectern. (chapter 75, p.7)
 * The entirety of the original Gundam series gets played out in Keima's intergalactic war between the single- and multi-heroine armies, right down to Char and Amuro's climatic sword fight. (chapter 75, p.10-14)
 * The year also corresponds with the timeline in the Universal Century. (chapter 75, p.11)
 * The key-shape of A Baoa Qu is an allusion to Leaf and Key. (chapter 75, p.11)
 * One of Zero's poses from Code Geass, played by Keima. (chapter 77, p.7)
 * Near's LEGO minifigs used to illustrate Keima's 3-step plan for capturing . (chapter 78, p.1)
 * Saint Seiya style shogi battle between Diana and Keima. (chapter 78, p.3)
 * Keima questions how a retro game has any connection with shogi. (chapter 78, p.11)
 * Umm... Okaa-sama, was that Hokuto Hyakuretsu Ken? (chapter 83, p.8)
 * Soaring high... Keima is the Tower of Babel. (chapter 86, p.12)
 * The Ivory Tower... A world of intellectuals... (chapter 86, p.16)
 * "God Is Dead." our Otoshi-kami decried. (chapter 86, p.17)
 * The front cover of vol. 10 is a shout-out to The Return of Godzilla.
 * "The further away you are from each other, the stronger your feelings will become. It's like a Choro-Q love!!" (chapter 88, p.5)
 * When a Soul Level 4 Weiss appears, it spells: BIG TROUBLE. (chapter 89, p.5)
 * Ayumi and Chihiro perform a Cross Bomber on Keima. Note how his glasses are knocked off. Then they mercilessly stomp him with insults. Just look at them go. (chapter 89, p.13)
 * Hinoki encourages Keima, "Boys, be ambitious!!" (chapter 91, p.16)
 * Keima drawn with Pablo Picasso's surrealistic gusto from "Guernica". (chapter 92, p.2)
 * Reappearance of Keima-Takahashi. (chapter 92, p.12)
 * Intentional or not, but when a character shouts "Urusai, urusai, urusai!!", it reminds you of that red-haired loli. (chapter 92, p.13)
 * Elsie is watching Magnum Robo Gashigo on the TV. (chapter 93, p.4)
 * A Pastiche of classic 70s mecha anime: The mock title identical to "Magne Robo Gakeen", Rocket Punch from Mazinger Z, and who knows how many others.
 * You know you heard it when you saw it... "Rider Kick!!" (chapter 93, p.12)
 * The chapter cover is from Shinkenzemi, an online study course. (chapter 94, p.1)
 * The opening song lyrics are from the Kougaman anime segment, which features cameos from Kyokyoku Chojin R. (chapter 94, p.4)
 * The two mascots are from Ponkickies, while the background is a homage shot to the SF anime genre. (chapter 94, p.5)
 * Keima's face when he throws the letter is the face of Yuuki-sensei. (chapter 94, p.6)
 * Eeney, meeney, miney, Keima-Moai. (chapter 94, p.9)
 * Silhouettes of Doraemon, Nobita, and Shizuka. (chapter 94, p.10)
 * It's unintentional, but Keima's face is from Kaitei Jinrui Anchovie, a manga by Yasunaga Kouichirou. (chapter 94, p.10)
 * Elsie's art style is from Love Cocktail. (chapter 94, p.14)
 * BGM "The Nearness of You" by Hoagy Carmichael & Ned Washington on the second panel.
 * The kites are from Nipponkodo's incense stick commercial. (chapter 94, p.17)
 * At the end credits Elsie sticks a disclaimer notifying Keima's comments are fictitious, referencing the events in The Sigh of Haruhi Suzumiya. (chapter 94, p.18)
 * Keima-Tarao: "An Anime?!" (chapter 94, p.19)
 * Tarao Fuguta from Machiko Hasegawa's Japanese comic strip Sazae-san.
 * Pac-Man as the runaway spirit and the pellets as its food. (chapter 96, p.8)
 * The vertical sign that reads "IOIO". An allusion to The Bee Gees' second single "I.O.I.O." from their seventh album Cucumber Castles. (chapter 97, p.2)
 * "Just according to plan..." states Kira Kusunoki. (chapter 97, p.15)
 * "The iron hammer of evil... will be swung down on the impure and filthy new devils!" Okay, seriously, we don't need any crazed implacable maids here. (chapter 97, p.16)
 * Original lines translated via formal equivalence: "To those impure and filthy new devils... The iron mace of evil!!"
 * The silhouette of Hinoki lovingly strangling Kusunoki. Hinoki sure does love her little sister! (chapter 99, p.13)
 * The first panel is awfully similar to the introduction in chapter 1, is it not? (chapter 104, p.1)
 * Due to an excessive rainfall, Japan Sinks! (chapter 104, p.5)
 *  (chapter 104, p.6)
 * Switch the earth in Keima's hand with an apple.
 * Thirsty for a sip of politics? Try the National Diet of Japan... with a fairy on top! (chapter 104, p.7)
 * Military general Keima from the Normal Game Department uses the famous quote from John S. Mill's book, "Utilitarianism": "It is better to be a human dissatisfied than a pig satisfied." (chapter 104, p.13)
 * One of the posters they're holding shows Nene Anegasaki from Love Plus, complete with a plus! (chapter 104, p.14)
 * The dominant 7#9 chord, colloquially known as the Hendrix chord. (chapter 107, p.1)
 * Keima has upgraded his game accessory to Virtual PFP 3D. (chapter 107, p.2)
 * Chihiro's punch sends Keima to the moon. (chapter 108, p.4)
 * It was one of those days, huh?
 * Love Romance Preparation Kit from... Tamiki. The stars in Tamiya Corporation's logo are replaced by hearts. (chapter 109, p.1)
 * Akari's shabby appearance and outworn backpack give her a striking resemblance to Asakura of Seikesshou Albatross. (chapter 109, p.17)
 * Keima imitates Peko-chan's face, the mascot of confectionary chain Fujiya Co. (chapter 110, p.15)
 * In the same chapter above, the nerds helping a small robot with a smiley face is actually based on an experiment in New York called tweenbots.
 * Allusions in Akari's Imagine Spot (chapter 112, p.9):
 * An ancient symbol of peace - The dove and the olive branch.
 * Not to be confused with the one from Noah's Ark and the Great Flood, though that is much disputed.
 * Genesis 3: Adam and Eve being expelled from the Garden of Eden, the Forbidden Fruit from the tree of knowledge, and the serpent.
 * Also, depending on your own interpretation, God's "pointing finger".
 * Why, if it isn't Keima as a certain leader of a certain political party of a certain country...
 * Keima's perfect human is just a Kewpie doll...with a convincing story to make it so. (chapter 113, p.2)
 * At the end of the Akari faux-arc, Nikaidou refers to the 1953 romantic comedy movie "Roman Holiday". (chapter 113, p.17)
 * The very first page of chapter 117 is a take on the Hell part of The Garden of Earthly Delights by Hieronymus Bosch.
 * Keima declares that he'll cease being a god and instead become a demon of the game world while adopting one of Lelouch's gestures. (chapter 121, p.19)
 * One of the chapter's segments is titled "A Hard Day's Night". (chapter 122b, p.6)
 * Professor Layton's emblem appears on the cover of the book Shiori is removing when she sees Keima on the other side of the shelf. (chapter 124, p.6)
 * Komaki Manaka can be seen on the cover of the Best 50 Dating Sims book. (chapter 124, pg.13)
 * Using The Game of Life to demonstrate the power of after-school events. (chapter 126, p.3)
 * Little Red Riding Hood Tsukiyo. (chapter 126, p.6)
 * Playboy Bunny Head Keima. (chapter 129, p.6)
 * When Keima explains that you should play games more often, the background is from Super Mario Bros.. (chapter 130, p.18)
 * Hinagiku can be seen on one of the posters. (chapter 131, p.13)
 * A recipe for vegetable soup by Cook[ing] Mama. (chapter 133, p.8)
 * KNN48. (chapter 137b, p.3)
 * Wakaki Tamiki-sensei, the author of TWGOK, seems to be really like Mitsuru Adachi-sensei. Besides the fact there are the most numerous and most obvious references to Adachi-sensei's works, Keima also makes a direct reference of Adachi-sensei's name. Unfortunately, I forget which chapter this was in but its in there somewhere.
 * The scenes that would had made it to the current anime were either altered or removed, most likely due to copyright issues and the fact that many current viewers may not be familiar with Adachi-sensei's works.
 * "I have no interest in humans." (chapter 140, p.11)
 * A railroad-variant of Pipe Mania. (chapter 172, p.4)
 * Keima describes how agile and fast Ayumi is by using a map made of squares with colored representing how far they can go. Keima, who is in the trees, cannot go as far as Ayumi. (chapter 174, p.6)
 * The Mai High Festival Arc revolves around three days where the hero must awaken ancient beings to help save the world from the end of the world occurring at dawn after the third day. Now if Keima or someone in Ayumi's band only played an ocarina.
 * Keima says that right now they need to think how to raise an Idol when Kanon is stabbed by the Vintage, then Haqua calls him on it, saying it's not time to think about games.
 * Keima is dressed up as Conan on the back cover of volume 16. (Chapter 156.5, Bonus materials)

In The Chapter Titles
Chapters are called FLAGs, referring to the corresponding mechanism in games.
 * FLAG.03 "Baby You're A Rich Girl": "Baby, You're a Rich Man" by The Beatles
 * FLAG.04 "Drive My Car" by The Beatles
 * FLAG.05 "I Don't Want to Spoil the Party" by The Beatles
 * FLAG.07 "IDOL BOMB!": Japanese Idol magazine "BOMB"
 * FLAG.08 "UP TO BOY": Japanese Idol magazine "UTB"
 * FLAG.10 "Shining Star": Japanese Idol magazine
 * FLAG.13 "The Inside and Outside of a Big Wall (大きな壁の中と外)": A novel by Arai Motoko
 * FLAG.14 "Inside of Me (私のなかの･･････)" - A novel by Arai Motoko
 * FLAG.15 "Open the Door (扉を開けて)" - A novel by Arai Motoko
 * FLAG.16 "The Last Day (おしまいの日)" - A novel by Arai Motoko
 * FLAG.28 "Rainy Days And Mondays" by The Carpenters
 * FLAG.29 "If You Find Your Ways, it Always Rains (たどりついたらいつも雨ふり)" by Takuro Yoshida
 * FLAG.30 "If the Rain Stopped (雨がやんだら)" by Yukiji Asaoka
 * FLAG.31 "10% Expected Rainfall (10%の雨予報)" by H20, also OP for the anime "Miyuki"
 * FLAG.32 "Singing in the Rain" by Arthur Freed and Nacio Herb Brown
 * FLAG.34 "Demolish the Bricks (つみき くずし)" - Japanese TV drama
 * FLAG.35 "The Dawn of Something (なにかの☆よあけ)" - Japanese TV drama or Variety Program
 * FLAG.37 "2年B組長瀬先生" - Parody of Japanese TV drama
 * FLAG.38 "School Wars (スクール☆ウォーズ)" - Japanese TV drama
 * FLAG.39 "Eager Times (熱中時代)" - Japanese TV drama
 * FLAG.40 "Scrapped Teacher (スクラップト・ティーチャー)" - Parody of Japanese school drama
 * FLAG.41 "In the Heart, the Sun Will Always... (いつも心に太陽を)" - Japanese title for "To Sir, with Love (1967)"
 * FLAG.44 "The Half Moon is the Color of Love (ハーフムーンはときめき色)" by Minami Syouko
 * FLAG.45 "The Moon and a Glove (月とテブクロ)" by Kinniku Shōjo Tai (KING-SHOW)
 * FLAG.46 "Mr. Moonlight" by The Beatles
 * FLAG.47 "The Girl's Her (彼女の彼)" by Watanabe Misato
 * FLAG.48 "Kano-Kano (彼女彼女の事情)": Parody of Masami Tsuda's "Kare Kano"
 * FLAG.49 "Kano x Kano x Kare (彼女X彼女X彼)" - Parody of CROSS-NET's galge "彼女&Atilde;—彼女&Atilde;—彼女"
 * FLAG.50-53 "H2O", "Touch", "Slow Step", "Mostly Sunny": Adachi-sensei called, he wants his copyright fee.
 * FLAG.55 "Help!" by The Beatles
 * FLAG.66 "Nights in White Satin" by The Moody Blues
 * FLAG.67 "Ride My See-Saw" by The Moody Blues
 * FLAG.68 "Every Good Girl Deserves Favour" - Parody of The Moody Blues' sixth album "Every Good Boy Deserves Favour"
 * FLAG.73~74 "The Escape from the Seraglio", "The Magic Flute" by Wolfgang Amadeus Mozart
 * FLAG.75 "Summer Wars" by Mamoru Hosoda
 * FLAG.80 "Pajama de Ojama" by Watase Yuu
 * FLAG.81 "Young Girl, Young Boy (少女・少年)" by Yabuuchi Yuu
 * FLAG.82 "She and My Eye×Eye" (僕と彼女の目X目) - Parody of Ai Morinaga's "Boku to Kanojo no XXX"
 * FLAG.83 "If Only I Could Exchange Them (とりかへばや)" - Reference to the literary work "Torikaebaya Monogatari"
 * FLAG.84 "Pretty Faces" - Reference to Yasuhiro Kano's "Pretty Face"
 * FLAG.85 "Twinkle Trick Star" - Parody of Hikaru Toyama's "Twinkle Twinkle Idol Star"
 * FLAG.86 "I'm That Guy and the Heroine is Inside Me" - Parody of Hisashi Yamanaka's children's literature "I Are You, You Am Me"
 * FLAG.87 "Princess Doubt" - Probably a twist on "Princess Debut"
 * FLAG.88 "Body Jack" - Reference to "Body Jack - Tanoshii Yutai Ridatsu"
 * FLAG.89 "Turn A" - Could be a direct reference to Turn a Gundam.
 * FLAG.102 "Devil May Cry" - An allusion with potential foreshadowing and wordplay?
 * FLAG.105 "Triangle Love Letter" by Triangle
 * FLAG.106 "Three of a Perfect Pair", album/song by King Crimson
 * FLAG.107 "Run Run Run" by the Velvet Underground
 * FLAG.108 "Venus in Furs" by the Velvet Underground
 * FLAG.110 "Do Androids Dream of Chicken Cutlets?" - An allusion to the sci-fi novel by Philip Dick, Do Androids Dream of Electric Sheep?
 * FLAG.111 "Mannequin" - Could be a reference to the movie
 * FLAG.112 "Absolute Girlfriend" - An allusion to the shojo manga Absolute Boyfriend by Yuu Watase
 * FLAG.113 "A・I" - A reference to the sci-fi film A.I.: Artificial Intelligence. Based on the short story "Super-Toys Last All Summer Long" by Brian Aldiss
 * FLAG.114 "Apollo"
 * FLAG.115 "Debris of the Sun" by Yutaka Ozaki
 * FLAG.118 "Scramble Formation" - Known as "Tokio" Japan, it's a 1986 Shoot'em-Up game developed by Taito Corp
 * FLAG.119 "Look Back in Anger" by David Bowie and Brian Eno
 * FLAG.129 "Close to the Edge" by Yes
 * FLAG.130 "Cheap Trick" - one of the best known Power Pop bands and quite popular in Japan
 * FLAG.134 "Strike Witches"
 * FLAG.145 "Close Romantic Encounters of the Third Kind"
 * FLAG.149 "About Me" by Shizuka Kudo
 * FLAG.153 "I, Me, 'My'ne" - play on "I, Me, Mine" by The Beatles
 * FLAG.154 "Play the Game" by Queen
 * FLAG.159 "Aqua Lung" by Jethro Tull
 * FLAG.171 "For a Few Lovers More" - A wordplay on For a Few Dollars More from the Dollars Trilogy by Sergio Leone.
 * FLAG.172 "The Good, The Bad, and The Ugly" by Sergio Leone.
 * FLAG.178-2 "Once Upon A Time in Majima" - Based on Once Upon a Time in the West by Sergio Leone

In The Anime

 * Miscellaneous
 * In the second PV, there are two books with particularly interesting titles in Shiori's kiss scene. The title of the first book is "[V]incent Law", a reference to the sci-fi anime the studio in charge has worked on. The second one, with the title "Bushido", is an allusion to Nitobe Inazo.
 * The theming is very much like another What Do You Mean It's Not Awesome? series, Trauma Center (fittingly, it's a game).
 * The pronunciation of "Elsie" in Japanese and English is pronounced similarly to "NPC." Fitting, considering that Elsie is actually from the Demon World, and that Keima will only work with characters not from this world.
 * "Haqua" can be pronounced in both English and Japanese similarly to "Hacker," as in computer hacker. Again, it's fitting, considering her past and her not-so-secret love for Keima.

Season 1

 * Episode 1
 * The main character accepts his "contract" to catch "loose souls" while saying "Ore wa no dare da to omote yagaru." In its English version, we know this as "Just who the hell do you think I am?!"
 * Just before that, we get a peek at his mail and he has an email signed by Konoha Sakura.
 * Episode 2
 * Chapter 2's BMW metaphor and Peanuts Art Shift. The 6-series model was altered by changing out its front fascia with that of the late-production E46 3-series.
 * Elsea says "I'm one hell of a little sister!", a reference to Black Butler.
 * Episode 3
 * When Mio is asked what she would do for lunch, she responds "If there is no bread, let me eat sweets."
 * Keima teaches Elsie something useful...along with a loud and clear shout-out to the opening of Heidi, Girl of the Alps.
 * A Zaku head on the fourth day, an interstellar locomotive on the fifth day, and a pumpkin carriage. (From chapters 4 & 5)
 * Keima (learning to waltz): Up, Up, Down, Down, L, R, L...
 * Episode 4
 * "So, as I play - Unlimited Blade Works!" (From chapter 6)
 * The background music during Keima and Elsie's commentary about the game sounds similar to "Gonna Fly Now" from Rocky.
 * The background music, while Keima is illustrating what a loop bug is to Elsie, is similar to, if not the same as, "Raiders' March" from [Raiders of the Lost Ark.
 * As the people who have failed to clear Sora's route are shown, this piece of music by Frederic Chopin is heard: Piano Sonata No.2 in B Flat Minor Op. 35, 3rd movement, Marche funebre: Lento.
 * Keima does Lelouch's signature pose, with the determination to clear Sora's route.
 * The illustration in the preview is by Misato Mitsumi, who was the character designer for To Heart 2... And on Keima's PFP screen is Konomi Yuzuhara.
 * Episode 5
 * Keima's Game Idol rally goes full-on Gihren Zabi.
 * Episode 6
 * Kanon's pet turtle is named Keitaro
 * Episode 7
 * Kanon's descent as Elsie wonders how they can find someone who's invisible is a shout-out to the Major's descent from Ghost in the Shell.
 * Episode 8
 * Chapter 11's silhouettes.
 * The title of Keima's segment is "I Think, Therefore I Fantasize", a parody of René Descartes' famous quote "I think, therefore I am".
 * Episode 9
 * The arrival of the Black Ships from chapter 13.
 * Keima henshins while shouting "KAAAMIIII NOOOOMIIII" with all the original sound effects.
 * Episode 10
 * During the library club's meeting regarding adding a new electronic media section, someone suggests Idol Master and Dead or Alive to be part of the check-out material.
 * Shiori quotes Otto von Bismarck: "Only a fool learns from his own mistakes. The wise man learns from the mistakes of others." (There's a similar quote in the manga, chapter 14, p.17, but it seems to be garbled by the translation.)
 * Chapter 15's Black Jack shout-out becomes a full-on Imagine Spot, with Keima as Black Jack and Elsie as Pinoko.
 * Episode 11
 * At one point, Shiori is reading a novel called Ergo Proxy.
 * Episode 12
 * Dejiko can be seen running during an Imagine Spot between Elsie and Keima.
 * Keima's secret technique has him wailing on all six of his game controlers, feet in the air like Fubuki. Mercifully the associated Fan Service was not included.
 * Later, when Elsie recalls what she saw, Keima was wearing a certain Red Jacket...
 * Hey... I don't remember playing that game with horses...

Season 2

 * Episode 1
 * The Re Cap sequence is based on Dragon Quest II.
 * Somehow has a shout out to itself "Wait. Didn't you watch the first season?"
 * Episode 7
 * Elsea briefly turned into a South Park character.
 * Episode 8
 * When Keima started to explain to Elsie the history of dating sim games, you can see an 8-bit Erza Scarlet running in the background.
 * Episode 10
 * There's a Dragon Age poster in the P.F.P. game Nikado is playing.
 * The same game is quoting Asuka in the infamous High School AU scene in Neon Genesis Evangelion.
 * Episode 12
 * Keima compares dating-sim heroines to The Girl Who Leapt Through Time, with himself in the place of that character.
 * "B's Ware" or does that actually mean BioWare?
 * It's a Shout-Out to Key, considering the logo has the same style (red underline and black alphabet). The fact that the game's scenario is amazing despite having a bad art style is a Shout-Out/Take That to Kanon.
 * Also, "B's ware" sounds like "Visual Art's" in Japanese.
 * Or could be from "C's Ware" who made games like Divi-dead.

Volume 1

 * Keima is dressed up as No Face, Elsee as Totoro and Amami as Nausicaa.
 * In the background, there are also tree spirits and karaoke machine with the song "Sanpo" from My Neighbor Totoro.
 * All of the allusions are works by Hayao Miyazaki and Studio Ghibli.

Volume 2

 * Aoba receives intensive training from Keima, who's wearing the whole "Coach" Ohta outfit.