Inyouchuu

A series of X-rated visual novels released by Tinkerbell, featuring art and character designs by Aojiru.

The plot of the first game (simply titled Inyouchuu, released in 2005) centers around Yamato Tachibana and Mikoto Shiratori, two part-time Demon Hunters who are assigned to go to a school and rescue Mikoto's sister Takeru, a co-worker who disappeared while on assignment at the school. After meeting Sui Kayama, an old friend of Yamato's, they exorcise the demons haunting the school.

The second game (Inyouchuu Shoku, 2006) has Mikoto, Takeru, and the newly recruited Sui go to a resort island to investigate a series of disappearances. They discover that

The third game (Inyouchuu Etsu, 2009) centers around events in Mikoto and Takeru's hometown, where they and Yamato must uncover the secrets surrounding the town chief and Azumi, a demon with connections to Yamato's past.

All three games are rather extreme, so discretion is very much advised. All three games have two episode OVA series based on them. There are also several tie-in  light novels and manga of varying length that cover both the material in the games and original material.

Inyouchuu contains examples of

 * Bifauxnen: Takeru's character design in the first two games.
 * Black Bra And Panties: Takeru wears black lingerie (and a rather daring swimsuit), but this seems more to highlight her status as the single most mature good human in the cast for the first two games.
 * Boobs Of Steel: Zig-zagged. Mikoto uses a sword and has an impressive bust, flatter Takeru primarily uses ofuda, while Sui is a Squishy Wizard in more ways than one.
 * Different As Night And Day: The Shiratori twins. Mikoto is headstrong, reckless, and easy to anger. Takeru is calm and analytical.
 * Dirty Old Man: Yoru, a cat spirit and Mikoto, Takeru, and Yamato's boss, gets this characterization.
 * Downer Ending: The OVAs and the manga feature the girls being enslaved by the Big Bad.
 * Face Full Of Alien Wing Wong: Happens in a number of the bad endings for all three games, and is intentionally used in the third game.
 * Gag Boobs: Sui.
 * Gender Blender Name: Mikoto is a unisex name, while Takeru tends to be a masculine name.
 * Hot Mom: Hatsune Shiratori, Mikoto and Takeru's mother.
 * Multiple Endings: Many Bad Ends in all three games.
 * Naughty Tentacles
 * No Canon For The Wicked: Shoku assumes the player got one of the good ends for the first game, while Etsu assumes the player got the best ending for Shoku. The OVAs are discontinuous and depict bad ends.
 * Only Sane Woman: In the first two games, Takeru seems to be the only good human with her head screwed on straight.
 * O Ring Orifice
 * Patient Childhood Love Interest: Sui to Yamato.
 * Potty Emergency: Early in Shoku, Sui needs to use the bathroom, but the line is very long. The player is given the choice to either stay in line or go by some out of the way rocks.
 * Squishy Wizard: Sui, in more ways than one.
 * Tsundere: Mikoto (Type 1)
 * Who Wants To Live Forever: