Noid: Ai no Sukuu Hoshi

In this world, a new alien species named Humanoids or "noids" roam the earth, indistinguishable from regular humans. However, the full moon triggers a transformation in them, though the shape they take differs between each noid. As such, noids are ostracized by society. Near seems to be one such noid and suddenly appears in the mountains where Keiji lives. With no identity and no memories, Near (named "Near" by Keiji) has nowhere to go. Keiji opens up his secluded home in the mountains to Near, knowing full well that what he was doing was a criminal act. But Near doesn't seem dangerous, and Keiji would love the company. It can get so lonely up in the mountains...

(Source: Fantasista Inc.)