
Ren, a nine-year-old left with no family after his mother's death, wanders the streets of Shibuya and slips into Jutengai, a world of beasts. There he is taken on as a disciple by Kumatetsu, gruff and friendless and a poor teacher. Renamed Kyuta, the boy grows strong while fighting with him constantly, but when he returns to the human world a darkness he has been carrying starts to surface.