Koakuma ga Miteta!

From MangaHelpers: Meguri Daiki found Ichigo, a doll sized cute girl devil, when he was still in high school. Now going to college and living on his own, he treats Ichigo as a pet/roommate and takes care of her needs, namely snacks and video games. Although Ichigo can’t talk, she seems to understand Daiki. He brings Tsuruoka Nei, a schoolmate from high school and now college, and gets intimate with her. But Daiki soon finds out that he isn’t the only one with a tiny devil as a companion.