Yami Kyun!

Miya Akatsuki appears to be an ordinary, somewhat irritable student at St. Margaret's Girls' College. In secret, she is a Final Executor, a specialized debt collector who ensures even the most uncooperative debtors agree to pay. The agency she works for operates in an unconventional manner. Haruki Kobayashi, who works in his family's electronics store, becomes involved with Miya after seeing her in action. As a precaution, Miya and two coworkers move into Haruki's home as part-time workers to monitor him. Over time, Haruki learns about the traumatic event that led Miya to seek power.