Tori no Kyuugaeshi

Synopsis

Kouta, an elementary school student who was isolated from his classmates due to his violent behavior, lost his temper one night in the mountains behind his school and threw a stone at a bird. The bird then appeared as a boy and declared that it would take "revenge" on Kouta. In exchange for throwing the stone, Kouta was forced to promise to "do whatever the bird says," and so he went to see the "bird" every night. (Source: Kadokawa, translated)