Sempai-Kohai

The concepts of sempai ("senior" or "upperclassman"; pronounced "sempai") and kouhai ("junior" or "underclassman") permeate Japanese society. They're most usually encountered in Anime in situations set in school, but the system also applies after graduation in the workplace. Older students (or workers with greater seniority) are known as sempai, and junior students/workers (or kouhai) are required to defer to them, and address them with the honorific -sempai. In return, the sempai is obligated to look out for, and protect, the kouhai.

Anime and Manga

 * In Yotsuba&!, Yanda is an old kohai of Koiwai's, and can get away with mooching off him for that reason. This only extends so far - when he picks on Yotsuba, Koiwai is obligated to pick on him in return.
 * In Super Dimension Fortress Macross, Hikaru calls Roy (who was a more senior pilot in Hikaru's family airshow) sempai.
 * In Robotech, this is changed to Rick calling him "Big Brother," which is not quite the same.
 * Maya Ibuki in Evangelion calls Ritsuko "sempai", which was given a whole new context in a scene in End of Evangelion.
 * Tatewaki Kunou in Ranma ½ yells at Ranma and other junior students whenever they fail to address him as "sempai". Even in the English dub, Akane always refers to Kuno as "Upperclassman Kuno".
 * Sei Suga in Mariasama ga Miteru is thrilled to receive a visit from current Lillian students at her office, as all of them are her kohai.
 * The Soeur system is based on this as well.
 * Hyatt and Elgala always refers to Excel as "Excel-sempai" in Excel Saga. In the dub, it's just "Senior".
 * Likewise, Milly refers to Meryl simply as "sempai" throughout Trigun, which is ironic considering Milly is almost as tall as Vash.
 * Yakou Tenma is the kohai of Pegasus in Yu-Gi-Oh! R.
 * In Digimon Adventure and 02, Jou is sometimes called "sempai," as he is the oldest of the group. Miyako also calls Koushirou "Izumi-sempai," as he was her senior in the computer club, and Daisuke refers to Taichi as "Taichi-sempai," as he was his senior in the soccer club.
 * Taiki himself becomes a sempai to Tagaru and Yuu in the sequel season to Xros Wars.
 * Shin of Dorohedoro is Noi's sempai. They happily makes bets on who will kill the most or eat the fastest. Despite being basically assassins, they're pretty decent guys. Shin only allows Noi to call him like that though.
 * In Code Geass, Andreas Darlton and Gilbert G.P. Guilford begin treating Suzaku Kururugi in a Sempai-Kohai fashion after he wins their respect, and even moreso after he's selected as Euphemia's Knight (they're both Knights of Euphemia's older sister Cornelia). In the second season, Guilford offers him some friendly advice and, when Suzaku expresses surprise, he openly admits to trying to play the sempai. (Despite the fact that in terms of status, Suzaku has surpassed Guilford at this point by becoming a Knight of the Round.)
 * Princess Cornelia, despite her royal status (she's officially fourth in line for the throne, and unofficially closer to second in line), treats Nonette Enneagram, the Knight of Nine, as her sempai in the audio dramas.
 * Subverted in Haruhi Suzumiya. Mikuru is Haruhi's sempai, but still gets The Chew Toy used like a dishrag by Haruhi.
 * In Ai Yori Aoshi, the university-going characters seem to be in the same year, but they have sempai/kohai relationships based on who joined the photography club first. Taeko always attaches "sempai" to Kaoru and Tina's names. Kaoru in turn is kohai to Tina and Those Two Guys, but he's close enough with them that he doesn't call them sempai.
 * In Naruto's ANBU, Kakashi is sempai to Yuugao and Yamato. He convinces Yamato to pay for a ramen lunch by suggesting that while he may be his sempai, Yamato is the only kohai he respects, and the two are essentially equals. Sakura refers to Shizune, Tsunade's first apprentice, as a sempai, and in an omake, Tsunade chides Shizune for not showing enough confidence in her junior disciple Sakura's chances of passing Kakashi's test. Suigetsu, an once-aspiring member of the Seven Mist Swordsmen, calls the members "sempai", despite the fact that his goal is to kill them and steal their weapons.
 * Ino refers to Shizune as "Shizune-sempai" in the anime, which plays up her involvement as a medical ninja and suggests that she learned medical ninjutsu from Tsunade. In the manga, she just calls her "Shizune-san".
 * Pain jokes that as they shared a master, Naruto should consider him his Sempai. Naruto is not amused.
 * In Bleach, Izuru, Momo and Renji consider Shuuhei their sempai; they first interact with him while he is directing a field exercise in their time in the Academy. Yoruichi refers to herself as Soifon's sempai.
 * In Yu Yu Hakusho, Yusuke initially greets Sensui as "sempai," as he was the previous Spirit Detective, but he's being sarcastic, because Sensui is now attempting to destroy the world and commit genocide. (Sort of.) Later, when Yusuke meets Kuroko Sanada, the first Spirit Detective, who retired with a modicum of her sanity in tact, he is incredibly respectful towards her, although he addresses her as "Kuroko-san," not "sempai." Either way, it's the most (conventionally...) respectful Yusuke is to anyone, ever.
 * In Minami-ke, Kana passes off "Mako-chan" as a kohai of hers in order to explain why a girl Chiaki's age keeps visiting her. Meanwhile, Haruka and her friends deal with Hosaka, whose attentions are unwanted but can't just be ignored because he's their sempai.
 * Azumanga Daioh: When the girls start their second year, Chiyo-chan is furious at not being taken seriously by the new freshmen (who are of course still older than her). She finally accosts a random student on the stairs and makes him call her "Mihama-sempai", then walks off giggling at the sound of it. The official translations use "Miss Mihama".
 * In the dub, she makes him call her "Senior Mihama", a somewhat literal translation of it (like when she calls her classmates "Miss (Name)", instead of "(Name)-san"- for example, "Miss Osaka"). It should also be noted that he's not entirely "random"- in the anime he asks "What's a kid doing here?" which makes her think she's been denied the respect she deserves.
 * At the school where Strawberry Panic is set, each new student is assigned a pair of sempais whose room she'll have to clean regularly. Nagisa and Tamao get Chiyo as room temp, and Hikari and Yaya get Tsubomi. Later, the temp Shizuma and Rokujou had a couple of years ago turns out to be important to the story.
 * Tsukuyomi uses this with Setsuna in Mahou Sensei Negima, both being closely-aged and similar-in-power members of the Shinmeiryuu, with Setsuna being both slightly older and stronger. Its implied that Tsukuyomi merely uses this playfully, not having quite the level of respect the title would otherwise connotate.
 * And later on it becomes pretty freaking obvious.
 * In Magical Girl Lyrical Nanoha Striker S, Signum refers to herself as being the kohai of the renegade Zest when she encounters him since she used to be a member of the branch where he held rank as an officer.
 * At the end of A's, when Hayate mentions that she's joining the TSAB, she notes that it will make her Nanoha and Fate's kohai, although they never officially have that kind of relationship. Hayate even uses the term "kohai" in the English dub of that scene. Near the beginning of the season, Mary addresses Amy as "Amy-sempai".
 * In Vi Vid, Vivio refers to Einhart as her sempai, but calls her "Einhart-san" rather than "Einhart-sempai"
 * Used repeatedly in Prince of Tennis.
 * In Rurouni Kenshin, Shishio refers to Kenshin, the government's previous manslayer in the shadows, as his sempai. Similarly to the Yu Yu Hakusho example, he's being kind of snarky about it, as Kenshin is kind of trying to stop his grand plans now.
 * There's also an exchange (with Kenshin borderline channeling his dark Battousai personality) where Kenshin dismissively refers to Shishio as his kohai.
 * In Katekyo Hitman Reborn, Skull constantly refers to the other Arcobaleno as his sempai. He is the youngest, after all.
 * Fran and the other Varia as well.
 * In Love Hina, Shinobu frequently calls Keitaro sempai.
 * And it is about the * only* form of direct, non-grudging respect he ever gets from anyone. Until.
 * In the manga of Ghost in The Shell Bateau gets on Togusa's case (Togusa being the rookie of the pair) about not backing his sempai. Togusa replies that kind of thinking is obsolete. The translation used may actually be the most bizarre used yet, with "sempai" translated to "bishop."
 * In Chobits, Yumi is incessant in referring to Hideki as her Sempai, even in the English dub.
 * In Burn Up Scramble, Lilika calls both her teammates sempai, even right after drunkenly kissing Rio.
 * In Harukanaru Toki no Naka de, Shimon calls Tenma "sempai".
 * In K-On!, Asuza refers to the older members of the light music club as '-sempai', much to Yui's delight.
 * In Soul Eater, Stein always calls Spirit "sempai".
 * In Ouran High School Host Club Haruhi adds -sempai to her upperclassmen's names, or sometimes will just call them "sempai." Hikaru and Kaoru also use -sempai for their upperclassmen except for Tamaki who they affectionately mock with the name "Tono" (meaning "lord") in reference to his sometimes archaic-sounding speech (like an old feudal lord). For a workplace example, Haruhi's mother Kotoko was the sempai of Kousaka Yuki, the Suou company's lawyer.
 * In Bakuman｡, Iwase addresses Aoki as a sempai while they attend Tokyo University together, as Iwase is a freshman while Aoki is a graduate student. Hattori is Miura's sempai among the Shonen Jump editorial department.
 * Mangaka refer to more experienced ones as "sempai", as Takagi refers to veteran mangaka Arai as "Arai-sempai." Some of helpers decide to leave after hearing that he's going to "pick a fight with a sempai mangaka".
 * In Mai-Otome, each second-year Pearl Otome serves as an Onee-Sama to two Coral Otomes (on average, one of the two does not make it to the second year). While most are addressed as "-onee-sama," Nina and Arika refer to Nao, and other Pearl Otomes, as "-sempai."
 * In the English dub, this is translated as "big sister," with no difference given between -onee-sama and -sempai. Even the Meister Otome whom Arika calls "-san" get "Big Sister".
 * In the My-HiME sound drama, "As the Cherry Blossoms Bloom", Shizuru, believing that Natsuki will never return her feelings, decides to be a good friend and sempai to her, until the Carnival starts, causing her 1)to realize that Natsuki will die if Shizuru loses and 2)to gain some hope that Natsuki will accept her feelings. Yuuichi also refers to Reito as "Kanzaki-sempai" or just "sempai".
 * Satou Takanashi from WORKING!! only ever refers to Popurar Taneshima as "Sempai"(she doesn't reciprocate); this might have something to do with her being Older Than She Looks.
 * In Kochikame, Kankichi Ryotsu is often called Sempai by most of the fellow police officers.
 * Yu-Gi-Oh! GX: At the start of the second season, Juudai is thrilled to finally be one of the older students, especially during his first duel against Edo, who refers to Juudai as 'sempai'. A few episodes later, Edo's final words to Ryou in their Pro duel have him calling himself Ryou's sempai, since he's been in the Pro Leagues longer than Ryou has. After that, Edo switches to calling Juudai by his name instead of "sempai". Also, Kenzan continually refers to most of the older students with the sempai honorific (except for Juudai, who is his aniki).
 * In Durarara!!, Tom and Shizuo still hold something of a sempai-kohai relationship long after both of them have graduated from school (with Shizuo now working as Tom's bodyguard). When Tom hires another bodyguard alongside Shizuo, Shizuo is elated that he gets to have a kohai of his own, completely oblivious to the fact that said kohai is plotting to kill him.
 * In Hidamari Sketch, Sae and Hiro are Yuno's and Miyako's sempai. They all seem to get along pretty well, so they don't seem to treat it like an obligation. In volume 4 of the manga and the third season of the anime, they all get two new kouhai: Nori and Nazuna. (Incidentally, Yuno moved into the room occupied by Hiro and Sae's sempai, Misato.)
 * Keroro Gunsou: Tamama often refers to the older members as '-sempai'; the only one who doesn't get this treatment is his beloved Gunsou-san. Kururu also refers to Giroro as his sempai at times; in his case, however, this is more to antagonize by reminding him that the scientist is younger than him, yet Kururu outranks him.
 * In SHUFFLE!, Asa is Rin and Kaede's sempai, but tells Rin to stop calling her "Asa-sempai".
 * In the fifth episode of the anime for Welcome to The NHK, Satou refers to Hitomi exclusively as sempai during their meeting. At the end of it, Hitomi jokingly asks him if he still remembers her name.
 * In Puella Magi Madoka Magica, Mami is Madoka's and Sayaka's sempai, both in school, and as a Magical Girl. She becomes motivated to protect them because of this.
 * In Ore no Imouto ga Konna ni Kawaii Wake ga Nai!, becomes Kyousuke's kouhai in their school after she transfers. The episodes  focus on how their relationship grows.
 * Rather frustrating to fans of the ship is the example from Skip Beat!!. Kyouko and Ren, lead girl and lead guy respectively, have a sempai/kouhai relationship as Ren has been in show business longer than Kyouko has. It's also a romance series with the biggest Anchored Ships you've seen in a shoujo in a long time.
 * Planetes has Hachirota's sempai to Ai Tanabe's kouhai.
 * From the one time she's seen doing it, Konata seems to enjoy surprising first-years by status-dropping when she goes to see her cousin in her class. Given that Konata is still short and flat enough to look like she's not old enough to be in high school even after she later graduates, it's quite a shock.
 * Subverted in Axis Powers Hetalia: Hutt River claims to be Wy's sempai (translated as senior in scanlations), but Wy doesn't pay him much respect: she is less than willing to greet him when she goes by his home and she even agrees with Molossia when he calls Hutt River a "lameass bastard". Still, Hutt's ridiculously snobby attitude doesn't help.
 * Kagura and Ayase in Okusama wa Mahou Shoujo use these terms, even after Kagura has left the school.
 * Happens a lot with Boys Love Genre and Yaoi works, whether set in a school or an office environment. For example, Souchi's sempai to Morinaga's kouhai in the university in The Tyrant Falls in Love.
 * It also frequently shows up in yuri works, especially since they're often set in schools.

Fan Works

 * Much to Kyon's delight in Kyon: Big Damn Hero, Kanae addresses him as Sempai. Haruhi lampshades this extremely quickly. Kyon is also very protective of her, and treats her like his little sister.
 * As of Chapter 32, Kanae also refers to, which seems to provoke an interesting reaction...
 * In Drunkard's Walk VIII, main character Doug Sangnoir compares the self-organizing social structure of Hufflepuff House to multiple levels of sempai-kohai relationships, with almost everyone ion the house having both a mentor and someone whom they mentor.

Literature

 * In Michael Crichton's Rising Sun John Connor instructs Peter Smith that to the Japanese they will be interacting with, Connor will be sempai to Smith's kohai.
 * This is true of the movie version of Rising Sun as well. Smith, played by Wesley Snipes and renamed Webster, remarks "That wouldn't happen to mean 'master', would it?"

Live Action TV

 * Super Sentai:
 * Despite technically being the senior officer in Tokusou Sentai Dekaranger, Tetsu (DekaBreak) fondly refers to Red Ranger Ban as "sempai", mostly because Ban showed him a way to fulfill his duties with passion instead of the hardnosed indifference he was taught.
 * In the various Sentai team-ups, the members of the younger Sentai team tend to defer to the older, sempai team.
 * In Tomica Hero Rescue Force Hikaru commonly refers to Kyosuke, Rei and Juri as this until he found out that the teams Sixth Ranger was Da Chief he reffered to R5 as "Dai-Sempai".
 * Tomica Hero Rescue Fire has a similar example, Tatsuya refers to Hikaru and the rest of Rescue Force as "Sempai". As for the team itself, Tatsuya calls Yuuma his sempai, who is in turn seen as a sempai by Jun.
 * Invoked in Thirty Rock. After the death of his mentor, GE CEO Don Geiss, Jack Doneghy tells Liz Lemon that Geiss used to call him kohai in private, while Jack reciprocated, calling him sempai. Although Jack won't admit it, he is very shaken by Geiss' death (or more accurately, preservation in carbonite), masking it by working himself up at the possibility that he'll inherit something from Geiss. He inherits Argus, Geiss' pet peacock. Long story short,

Video Games

 * One set-type of double battle trainers in Pokémon is a pair of schoolgirls called "Sr. and Jr." ("Senpai and Kohai" in Japanese). The sempai is overly concerned with being a role model to the Kohai and the Kohai is overly concerned with impressing the sempai.
 * In Persona 4, Yosuke is surprised to find that the tough, rumored-to-be-in-a-biker-gang (he's not) Kanji is his kohai. He's also delighted when he finds out the cute and famous Rise is also his kohai when she attends the school. Unfortunately, Rise is more interested in your main character...
 * One of the big differences between Personas 3 and 4 is that in Persona 3, the main character trio are the underclassmen (although your main character gives orders in battle because he is the most skilled in the use of his Persona) and sempais Mitsuru and Akihiko are calling the shots (to the point where they won't allow you to do any missions if both are not present), but in Persona 4 the main character trio (and later Yukiko as well) are the sempais and are in charge of the entire investigation team with the later members as their underclassman. The only 3rd year with a name in Persona 4 is Saki, who's killed off early on.
 * In Pokémon Mystery Dungeon: Explorers of Time/Darkness/Sky, Bidoof is delighted when your team joins the guild, since his seniority makes him your sempai, despite his own inexperience.
 * In Kingdom Hearts: Chain of Memories, Axel gives a hearty "ja ne sempai" to before . He's likely being snarky about it, though, because the other Organization members simply address their elders by name.
 * The Tokimeki Memorial series, being a High School romance Dating Sim series, obviously loves this trope. Every flagship game of the series (save for Tokimeki Memorial 3) had a Kohai as a winnable Love Interest, and several side games introduced other non-winnable Kohai. However, winnable sempai weren't introduced until late in the series, the first one appearing in Tokimeki Memorial Girl's Side 2.

Visual Novels

 * In Tsukihime, Shiki calls Ciel "Sempai" almost exclusively, even in his narration. Arihiko does the same. One point where you notice this is the first scene after Ciel
 * Shirou is Sakura's sempai in Fate Stay Night. He takes this responsibility seriously, and it makes him feel a bit awkward about being attracted to her. Rin is also her sempai, and that's unfortunate—it's
 * Much like Shiki with Ciel, Sakura always refers to Shirou as "Sempai" (even when in the presense of other people who are also her Sempais, like Rin). Even in the HF True epilogue, where and he's no longer even her Sempai, she still uses it (and Taiga calls her out on it).
 * From the Girls Love Visual Novel Sono Hanabira ni Kuchizuke wo, we have Yuuna as sempai and Nanami as kohai as part of a Schoolgirl Lesbians pairing. Kaede and Sara are also sempai and kohai but it isn't emphasized as much.

Web Original

 * Jade from the Whateley Universe refers to her friends, particularly her roommate Tennyo, as 'sempai', and tends towards this kind of attitude.

Western Animation

 * As a part of the adaptation in the Japanese dubbed version of Peanuts, Marcie address Peppermint Patty as sempai, instead of "sir" like she normally does in the original version.