Jappa no Amane

From Kiwimyweewee:

A college student named Mitsuko works at his uncle’s hostel. On his way from an errand, he finds an unconscious yokai, Tenshi. When Tenshi wakes up he acts ferocious and arrogant. To express his gratitude to Mitsuko for saving his life, he also becomes a guest at the hostel on his own accord until Mitsuko decides what he wants. After being acquainted with Tenshi, gradually he opens his heart to Mitsuko. Suddenly Tenshi’s body transforms into an adult-like appearance and harasses Mitsuko!