Ore wa Maou-sama ni Moyamoya shitemasu

Char, a vampire demon king, and Haida, an ordinary police officer. They live together after they are almost killed in an encounter. The little boy Char has a secret: he will return to his adult form only for two days during the new moon. For those two days, he does not even ask Haida's permission, and makes him end up loving him as a “thank you” for all the good he has done for him. He always showers him with such sweet words as “he's cute” and “I want to be with him,” but Haida knows that Char has a daughter-in-law. All of this is just idle talk to pass the time. Haida knows this, but he is still bothered by it. What is Char's true intention...?