Toudaimori to Kamome no Ko

Atop the rocks of Claire Island, the lighthouse keeper Evan lives on his own, until a boat washes ashore carrying a dying seagull chick. After caring for it over the night, it was gone the next morning. And in its place was a curious winged boy that Evan names René. Though René looks human, he definitely isn't quite human. And his arrival begins to effect strange changes in Evan as well.

(Source: Taiyoh Tosho, translated)