The story intertwines two strange narratives: a mysterious "Doll" is captured and subjected to brutal torture by a Thunder Geist seeking information on an entity named Single, while a student named Asaki discovers his unnatural resilience after a truck accident, leading to a provocative sexual encounter with his school nurse. As these disparate events unfold, a mysterious figure emerges from the shadows to confront a boy in a local park.
After discovering that he is a uniquely powerful Geist-infected human, Hiroki forms an uneasy alliance with Shion, a dimensional "Doll" designed to hunt his kind. However, their relationship is put to the test when Shion is captured by a sadistic Slug Geist who uses a pleasure-inducing serum to torture her for information. Just as Shion reaches her limit, the mysterious leader of the Geists, Miko, makes a sudden appearance.
Following their battle with the Slug Geist, Shion and Hiroki share an intimate bond as Shion helps him manage the destructive urges of his Geist infection. However, their peace is shattered by Misuzu-sensei, who reveals that Hiroki will fully transform into a Geist within 24 hours. To save him, Shion forms an uneasy alliance with a resurrected, insect-like Odawara, leading them to the old school building for a confrontation with the Geist Mikuriyagawa-sensei.
After Misuzu-sensei provides the antidote to prevent his full transformation into a Geist, Hiroki enjoys a brief period of peace and intimacy with both her and Shion. However, this happiness is short-lived when Infinity, the Master of the Dolls, arrives to punish Shion for her betrayal. In a tragic confrontation, Shion is fatally wounded, leaving Hiroki with her final, heartbreaking plea to never forget her love.