(K)night & Day: The Stray Knight Has Made Love with Me Like a "Beast" in the End.

Sinopsis

Anna picks up Kei, a mysterious knight who has taken a reverse trip to modern Japan. Anna was getting used to strange cohabitation, but the sexual desire she had left over after half a year of masturbation abstinence was already at its limit... The man in front of her is polite but quiet, unfriendly, and stoic. Her curiosity begins to tingle. (Source: DLsite, translated)