In Fukai ni Nemuru Oujo no Abaddon Episode 1, viewers are introduced to a chilling narrative set within the enigmatic Ayakoji Mansion, nestled deep in a dark forest. The story begins with Professor Shoukei Yamanobe, a university professor and friend of the mansion's owner, who ventures into the mansion with his assistants to investigate its mysteries. Upon arrival, they realize they lack the keys to enter. Subsequently, Homura Yamanobe, the professor's son, arrives with his friends to deliver the keys, only to find his father missing. As they delve deeper into the mansion, they encounter two members of the professor's team, and the group decides to split up to search for him, unwittingly triggering a series of terrifying events. The episode masterfully builds suspense through its atmospheric setting and intricate character dynamics, blending elements of horror and mystery. The animation captures the eerie ambiance of the mansion, with detailed backgrounds and a muted color palette that enhances the sense of dread. Themes of curiosity leading to peril and the unknown lurking within familiar spaces are explored, offering viewers a gripping and immersive experience.