Akuma-ouji Kisoukyoku

On the night of the Demon King's death, Prince Zale leaves the castle to the pure demon Belphegor, who has been designated as the Soul Contractor. As Soul Contractor, he needs to get his hands on a "White Soul" of a human, which must be sought out and brought back. Thus, Prince Zale and his Watch Servant Haruka set out on a journey to the human world to search for this person. But, he didn't know that the magic of true "love" would be so overwhelming...

[From: Boys' Love Games Headquarters]