As a child, Shiki Toono sustained an injury that nearly killed him. Due to this incident, he was taken away from the Toono household and given to a relative for upbringing. Years later, when Shiki is in high school, his father dies, and Akiha, now the head of the household, orders him to return home. However, Shiki harbors a secret: since the accident, he has been seeing lines on objects, which can only be hidden with special glasses. He also struggles to remember anything from before the injury. On his first day back at the Toono household, Shiki encounters Arcueid Brunstud and accidentally decapitates her in a moment of temporary insanity. Later, she appears alive and asks him to protect her, marking the beginning of Shiki's quest to uncover the truth about his past.