Season 1 of Isaku premiered on November 28, 1997.

It's the last day of school before summer vacation. Kenta is gearing up for another boring summer when he receives a mysterious note. After school, he walks into the old, condemned school building, following the note's instructions. Inside, he finds that Jinpachi, Miyuki, Rika, Kotomi, Akemi, Ms. Kumi, Munemitsu and Mio have received the same note as well. Everyone decides that this is some kind of a joke, and starts arguing about the identity of the prankster. Suddenly, they hear the entrance being boarded up... The nightmare begins as the girls vanish one by one. Rika is the first one to disappear, followed by a shocking video of Rika being violated by an unknown assailant... A twisted story filled with scenes of shocking and graphic hardcore sex!!!

Season 2 of Isaku premiered on February 23, 2001.

Kotomi was looking forward to a fun summer vacation. Until she found the note in her bedroom. Filled with extremely personal and revealing information about her, Kotomi is forced to follow the note's instructions and go to the old school building. Once there, she discovers that she's not the only one.

Many of her classmates including the headstrong Miyuki are also there. But when everyone is suddenly trapped inside the building and girls start disappearing, it's only the beginning of the nightmare.

A tale of violence, perversion and lust, filled with hardcore sex and unusual sexual fetishes!