Ao Oni The Animation (2017)

Based on the horror game Ao Oni by noprops. Five members of the cultural anthropology club at an old western-style school are trying to come up with ideas for their presentation at the school's culture festival, when they find a collection of folk tales gathered by a student in their club 40 years ago. They realize that the mysterious Bellflower Oni that appears in the folk tales may be the basis for the popular free game Ao Oni, and decide to make that their theme. They manage to make contact with the author of the Ao Oni game, but he dies mysteriously soon afterward. The club members become suspicious at the author's death and began to investigate on their own, but encounter a secret they never should have touched: a secret underground prison in the school. For some reason all the fire doors at the school are locked, and they are trapped in the school. The sound of the strange footsteps they hear soon turn to their screams...A new tragedy of the Ao Oni is about to begin.

Unfortunately the movie Ao Oni The Animation is not yet available on HBO Max.