Guardian Dog Manga

Guardian Dog summary:

Kurosaka Kendo is just your normal high school boy, who likes to skip cleaning duty. But Gengo's peaceful life ends, when he one night meets a strange man. That man claims to be an alien and is in need of Gengo's body to survive on earth. Now, Gengo must not only deal with alien now resting inside of him, but also with other aliens, who for some reason seem to be after him!