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.
A história se passa em uma época em que o mundo está em completo desespero depois de ter sido devastado por um veneno chamado "Shinobi", que veio à Terra através de um asteróide. As pessoas fogem ao lugar chamado "Kairiku", um lugar que costumava ser o fundo do oceano. Aqui, as pessoas tentam se proteger contra os efeitos do veneno. Num mundo assim, não havia uma única luz de esperança. A "Arma Sagrada Giga Road" e o guerreiro lendário "Yagyuu" são agora necessários para combater os efeitos do veneno. Para salvar o mundo, Ame, uma princesa de uma nação caída, ergue-se, a fim de salvar o mundo.
