In the animated adaptation of Ao Oni, the storyline delves into traditional mystery horror akin to the original game. Set in a quiet town near a mountain forest, five students from the high school's folklore club stumble upon decades-old research notes left by a former member. Intrigued by the eerie resemblance between the documented legend and a popular game known as 'Ao Oni,' they decide to base their culture festival project on it. Upon meeting the game's developer, an unexpected tragedy strikes as the creator meets a sudden demise. As the club investigates this enigmatic death within the school premises, they soon find themselves trapped inside with no means of escape.