Isaku

Isaku (遺作) is a hentai survival horror game released for DOS in 1995. A Windows version and a sequel, Shusaku, were released in 1997. A sequel to Shusaku was released on PC in 2001 going by the name of Kisaku. An anime series based on the games was also released in 1997.

Story and Gameplay
The objective of the game is to have the player and his companions escape from a locked school building while avoiding being captured by Isaku, the villainous school gardener.

The player takes the role of Kenta, a high school student trapped by Isaku on the fourth floor of an abandoned school building together with several schoolmates and a teacher. The only way out is through a stairwell, the doors of which are locked on every floor. The player must search the rooms on each floor for clues and items that will lead him to locate the keys that will open the stairwell doors and allow the party to descend to the next level.

Throughout the search, the player must also make sure that none of his companions - particularly the girls - are abducted by Isaku. Although it is still possible to escape even if Isaku manages to capture one (or most) of the party, neither of the two possible "good" endings can be subsequently attained. Should a character be abducted by Isaku, the player may eventually come across a video tape that contains a recording of a rape scene between Isaku and his unfortunate victim.

While primarily a puzzle-solving game, a form of dating simulation has also been integrated, allowing the player to select one of two girls to end up with romantically at the conclusion of the game.