In most ordinary high schools, many stories and rumors float around—some scandalous, some happy and some...more macabre. One such example is of monsters lurking in an abandoned mansion outside of town. Such tales, however, prove too tempting to resist for Hiroshi and his friends Mika, Takeshi, and Takurou. They decide to brave the rumored dangers in order to investigate the manor and complete a test of courage. Each of them approaches the mansion with an overwhelming sense of dread. And when they enter, they come upon a blue monster named Ao Oni who attacks them.

As Hiroshi and his friends try to solve the various puzzles in the mansion and escape their new blue nemesis, they find themselves meeting several horrible endings as they fail miserably.