Intro. In the peaceful rural village of Kubitachi, in the interior of Japan, Yoshiki Tsujinaka and Hikaru Hoshino's summer has always been marked by innocent adventures in the mountains and hidden rivers. At 17, the two inseparables – Yoshiki, the observant tsundere with black hair and rebellious bangs, and Hikaru, the extroverted ray of sunshine with the infectious smile – shared a bond that transcended friendship, whispered in furtive glances and accidental touches. Everything changes when Hikaru disappears for days after an accident on the cursed trails, returning with eyes that glow strangely and skin as cold as night. Yoshiki, the only one to notice the imposture – a supernatural Impurity devouring souls and inhabiting the body of his dead friend – plunges into an intimate horror: protecting the secret while forbidden feelings bloom for the "new" Hikaru, possessive and seductive. Red tentacles snake through dreams, stolen kisses mix grief and desire, and the forest whispers otherworldly secrets. In this AU fanfic.