Etou, a socially withdrawn student with a crush on the popular honor student Miyamura Sayoko, discovers her shocking secret after saving her from a group of thugs. Sayoko possesses a bold, provocative split personality named Yako, who leads Etou into a series of daring encounters. Guided by the philosophy of "memento mori," Etou finds newfound confidence while Sayoko begins to question the restrictive expectations of her perfect public image.
Mutou discovers the tragic origin of Miyamura's split personality and shares a bittersweet final encounter with Yako, who is slowly disappearing as Miyamura reclaims her psyche. Meanwhile, the domineering Origasa manipulates her former teacher into a subservient relationship to fill a void in her heart, eventually finding a strange sense of belonging with both the man and her long-lost dog.