One Room, Hiatari Futsuu, Tenshi-tsuki.

After a long day, high schooler Shintaro Tokumitsu's plans for relaxing in his studio apartment take a turn when he discovers an angel on his balcony. The divine girl, Towa, reveals she's there to study humanity, and yet, despite his skepticism, he agrees to put her up. Prepare for the most heavenly and high jinks roommate experience of all time!