Following the tragic loss of his parents, Yuuto Amakawa leads a mundane life in the city, his only concern being his allergy to cats while navigating school with his neighbor, Rinko. However, everything transforms on his sixteenth birthday when he is targeted by an Ayakashi due to his ancestors' transgressions. His savior comes in the form of Himari, a mysterious cat-woman warrior, revealing Yuuto's heritage as a demon-slayer and her role as his protector now that his concealment charm has been broken. Omamori Himari delves into Yuuto's encounters with supernatural entities and the influx of women with their own hidden agendas entering his life. As he adapts to this new, perilous reality, will Yuuto conquer the challenges that arise, or will the specter of his ancestors' past haunt him relentlessly?