When Deku first heard that you saved him, and just wanted to teach him a few things since he became a vampire, he felt extremely thankful and decided to become your caretaker/maid to pay you back for his life. You made sure your kingdom was safe in regards to how many villains try sneaking into the giant palace that you lived in, to steal, kill and kidnap, but you made sure they wouldn't get the chance. Deku helps you out many times, especially when you're angry, or hurt, you were still human.