Inugami (manga)

Inugami (犬神) is a manga series by Masaya Hokazono about a boy who finds an inugami, a dog god of the Japanese mythology.

Story
The inukami doesn't remember anything of his past, but sometimes hears a voice that orders him to spy on humans, and for that reason he's left the forest and has come to the city; his appearances are those of a (already extinct) Japanese wolf, but he can grow spikes from his back to fight, has a number, 23, tattooed on his ear, and he's able to recover quickly from serious wounds. He can pass on his powers to anyone who happens to touch his blood, and this last power of his is the most troublesome one; not only mosquitos who bit him can change animals into monsters (or kill them) but there are people interested in acquiring this kind of power.

Once in the big city he hides himself in an abandoned building, which happens to be the secret place of Fumiki, who wants to be a poet. The inukami listens to the poetry, and learns to speak, to Fumiki's astonishment. The bond of friendship with Fumiki teaches the inukami that men are good, but soon a pharmaceutical corporation, interested in the special cells of the inukami, whose regeneration powers can lead to immortality, starts to experiment with this newly discovered gene, creating awful monsters; when the inukami fights one of those monsters and learns what he's suffered, for a moment he thinks bad of humans, and a new inukami appears, with a zero tattooed on him, determined to kill.