Ane Naru Mono is a supernatural horror manga series that revolves around the life of Yuu, a lonely orphan, who encounters Chiyo, an eldritch being. Chiyo promises to become Yuu's older sister, offering him warmth and companionship. However, her true nature and the dark world she belongs to pose mysterious and eerie challenges. The story explores themes of family, loneliness, and the unknown, blending heartwarming moments with unsettling horror elements.