18+ Asobi ni Iku yo!

The story revolves around Kakazu Kio, an ordinary high school freshman living in Okinawa. A girl with cat ears appears before him during a memorial service for one of his family ancestors. The girl calls herself Elis and claims she is an alien. Before long, fanatical alien worshipers and a mysterious government agency are in hot pursuit of Elis, but Kio's childhood friend Manami—who wants to follow in her father's footsteps in the CIA—captures Elis. Kio finds himself having to protect Elis from everyone.

(Source: Wikipedia)