Folklore no Gochisou

Shinobu, a kind-hearted boy who enjoys being around children, takes in Shion, a soaked and seemingly helpless boy found outside his home. After Shinobu cuts himself and Shion licks the blood from his finger, Shinobu experiences sudden physical reactions and heightened sensitivity. Shortly after, Shion transforms into an adult man and begins instructing Shinobu in various activities. As their interactions continue, Shion grows attached to Shinobu and decides to stay in his home.