I/O

Also known as I/O. This is the first original game by the company Regista, founded by Takumi Nakazawa of the Infinity series (Never 7, Ever 17, and Remember 11) fame, and a collaboration between Nakazawa and Romeo Tanaka (of Cross Channel, Kana Little Sister and Yume Miru Kusuri fame).

I/O takes place in the year 2032. A lunar eclipse occurs in late April, causing a surge of terrorist activities and bizarre incidents. As time goes on, things get worse and worse, with the key to the mystery seemed to be locked away in the MMORPG "Babylon". Four people, through their own ways, investigate the ongoing phenomenon, each one dealing with his or her own problems...

I/O, like the Infinity series, has multiple protagonists, in this case four. Route A features Hinata Aoi, an Ordinary High School Student who has become depressed after the disappearance of his twin sister, Mutsuki. Route B features Ishtar, a young woman in charge of a hacking group known as Criminal. Route C also features Ishtar, but she seems different from herself in Route B. Route D features "He", a mysterious man who is a legend on the Internet. Once all four of their routes have been completed, they unlock Route E, the true route.

The game was originally released on the Play Station 2 in 2006, but was given an Updated Rerelease on the PC two years later, with new CGs and slightly updated artwork.

This game provides examples of:

 * Ambiguous Gender- Enlil, who is never specifically identified as a man or a woman.
 * Arc Words- "The beginning is the end, and the end is the beginning."
 * Artificial Human-
 * Ascend to A Higher Plane of Existence-
 * Badass- "He" lives and breathes this trope.
 * Badass Longcoat- Once again, "He".
 * Big Bad-
 * Bittersweet Ending-
 * Bolivian Army Cliffhanger: If you haven't cleared the routes required to see their full endings, Route B and C end this way.
 * Brilliant but Lazy- Hinata is very intelligent and is shown to be able to solve complicated problems in seconds, but he's so apathetic towards life that he's just not interested in it (much to Sakuya's consternation).
 * Brother Sister Incest- While nothing explicit happens, there's a lot of subtext between Hinata and Mutsuki, who is practically obssessed with his sister. Lampshaded several times, particularly where he questions Yayoi whether or not he has a sister complex.
 * Butt Monkey- Kosuke, who seems to exist to get verbally abused by the other members of Criminal.
 * Chekhov's Gun-
 * Chekhov's Gunman-
 * Contemplate Our Navels- The characters go into this occasionally, especially towards the end of Route E.
 * Cool Shades- "He" has a pair.
 * The Cracker- The cyberterrorist group "Code" is composed of these.
 * Cyberspace
 * The Danza- Kosuke Miyata, who is played by Kosuke Toriumi.
 * Disappears Into Light-
 * Driven to Suicide-
 * Drowning My Sorrows-
 * Downer Ending-
 * Emergency Transformation-
 * Eye Scream
 * Eyes Always Shut- Ningirsu.
 * Forgotten Fallen Friend-
 * Genki Girl- Lem, the fairy from Babylon.
 * Goggles Do Nothing- Route C Ishtar wears a pair of goggles/sunglasses on her head that she never wears.
 * Guide Dang It- This game is incredibly difficult to clear if you have no idea what you're doing.
 * Specifically, there are initially four routes. Sounds simple enough. What the game doesn't tell you is that you have to get a certain other ending to see the full ending of another route. If you don't, then you are left at a "cutoff point", which seems like the ending, but isn't. (In order to see Route A's full ending, you have to clear Route C, Route D must be cleared to see Route B's full ending, Route B needs to be cleared for Route C's ending, and Route A needs to be cleared for Route D's ending). Then you unlock Route E, which, if you clear that, opens up four new routes which must be cleared, and it is then and only then that you can see the True Ending. Sound complicated?
 * Gun Porn- One scene in particular in Route D is practically devoted to discussing the specs of "He"'s weapons in great detail.
 * Half Identical Twins: Hinata and Mutsuki have very similar body structures despite being fraternal twins.
 * Heroic Sacrifice-
 * Hey Its That Voice
 * Perhaps due to Romeo Tanaka's influence, this game shares several voice actors with Yume Miru Kusuri, such as Michihiko Hagi (who voices Hinata in I/O and Takeshi in YMK), Ryoko Tanaka (who voices Sakuya in I/O and Mizuki in YMK), and Kayo Nagata (who voices Mutsuki in I/O and Nekoko in YMK). Incidentally, the two games were released a month apart from each other.
 * Hope Spot-
 * I Want My Beloved to Be Happy-
 * Inferiority Superiority Complex-
 * Its Not You Its My Enemies-
 * Japanese Ranguage- Actually used as a plot point once.
 * Journey to The Center of The Mind-
 * Les Yay- Mika seems to look up to Ishtar a little too much at times, with later routes making it quite clear that she views Ishtar as more than just a friend.
 * May December Romance-
 * Meaningful Name- Several, some of them Lampshaded in-story, while others come from Word of God:
 * When reversed, the kanji in Hinata Aoi's name forms the kanji for "sunflower".
 * The kanji in Mutsuki's name literally mean "dreaming moon".
 * If you take out the middle kanji in both Mayumi and Masami's names, you get the kanji for "truth". This is explicitly pointed out by Ishtar at one point.
 * Mesopotamian Mythology- A major theme in the game, with characters, locations, and terms being named after Babylonian and Assyrian mythological terms.
 * Mismatched Eyes- Ishtar, who is specifically noted to have heterochromie.
 * Oblivious to Love- Hinata seems completely unaware of Sakuya's rather obvious feelings for him.
 * One Steve Limit: Subverted,
 * Playful Hacker- Many, but especially Ishtar, who one time manages to make a program to delete viruses like a shooting mini-game.
 * Put On a Bus- After the end of Route A, Sakuya just disappears from the plot altogether.
 * Rapunzel Hair- Ishtar.
 * Refusal of the Call-
 * Robotic Reveal-
 * Sacrificial Lion-
 * Shrinking Violet- Mayumi.
 * Shout Out- A subtle one to Ever 17.
 * There are more to various pieces of literature, such as Alice in Wonderland, The Once and Future King, Macbeth, The Epic of Gilgamesh, A Connecticut Yankee in King Arthurs Court, Do Androids Dream Of Electric Sheep... the list goes on.
 * Soundtrack Dissonance- "Subnetwork", a rather calm, soothing theme... which often plays as something bad is happening or when people are dying.
 * Stalker With a Crush- Andras to Mika, which traumatizes her horribly.
 * Sunglasses At Night- "He" always wears sunglasses, regardless of time or place.
 * Surprisingly Good English- With a few exceptions, the written English in the game is correct, both grammatically and spelling-wise.
 * Talking to Himself- Twins Mayumi and Masami Shinozuka, who share the same voice actress. There are also several other characters in the game who share voice actors, but that's more due to the limited voice cast rather than other reasons.
 * Take Up My Sword-
 * Taking the Bullet-
 * Cool Big Sis/ Team Mom- Ishtar for the rest of Criminal.
 * Technical Pacifist-
 * Theme Naming- Many characters, locations, and terms are named after entities from Babylonian/Assyrian mythology, and there are many allusions to said mythologies.
 * Tomato in The Mirror-
 * Took a Level In Badass-
 * Tragic Keepsake-
 * Tsundere- Sakuya for Hinata and Masami for Kosuke.
 * Twin Switch- In an additional scene in Route B,
 * Virtual Ghost- Shadow Nulls, who are essentially the remainders of someone who used Cyberspace frequently, and can continue to live after death in that world, but cannot interact with the real world unless they have someone living to do it through.
 * Yandere-
 * There are more to various pieces of literature, such as Alice in Wonderland, The Once and Future King, Macbeth, The Epic of Gilgamesh, A Connecticut Yankee in King Arthurs Court, Do Androids Dream Of Electric Sheep... the list goes on.
 * Soundtrack Dissonance- "Subnetwork", a rather calm, soothing theme... which often plays as something bad is happening or when people are dying.
 * Stalker With a Crush- Andras to Mika, which traumatizes her horribly.
 * Sunglasses At Night- "He" always wears sunglasses, regardless of time or place.
 * Surprisingly Good English- With a few exceptions, the written English in the game is correct, both grammatically and spelling-wise.
 * Talking to Himself- Twins Mayumi and Masami Shinozuka, who share the same voice actress. There are also several other characters in the game who share voice actors, but that's more due to the limited voice cast rather than other reasons.
 * Take Up My Sword-
 * Taking the Bullet-
 * Cool Big Sis/ Team Mom- Ishtar for the rest of Criminal.
 * Technical Pacifist-
 * Theme Naming- Many characters, locations, and terms are named after entities from Babylonian/Assyrian mythology, and there are many allusions to said mythologies.
 * Tomato in The Mirror-
 * Took a Level In Badass-
 * Tragic Keepsake-
 * Tsundere- Sakuya for Hinata and Masami for Kosuke.
 * Twin Switch- In an additional scene in Route B,
 * Virtual Ghost- Shadow Nulls, who are essentially the remainders of someone who used Cyberspace frequently, and can continue to live after death in that world, but cannot interact with the real world unless they have someone living to do it through.
 * Yandere-
 * Tragic Keepsake-
 * Tsundere- Sakuya for Hinata and Masami for Kosuke.
 * Twin Switch- In an additional scene in Route B,
 * Virtual Ghost- Shadow Nulls, who are essentially the remainders of someone who used Cyberspace frequently, and can continue to live after death in that world, but cannot interact with the real world unless they have someone living to do it through.
 * Yandere-
 * Yandere-
 * Yandere-