Maou-sama no Mou Approach ga Overkill sugimasu

Despite his unfortunate constitution, Yuuta Yuuki has lived a rather ordinary life. Recently, he has been having strange dreams where he sees someone crying. One day, Rei Masaki, a transfer student, suddenly appears before Yuuta. Although it was the first time they met, Rei has a strange sense of distance between him and Yuuta. As it turns out, Yuuta was a hero in another world in his previous life. Furthermore, he and the demon king were lovers...!? A modern reincarnation love story between a handsome demon lord and an unfortunate former hero! (Source: Kadokawa, translated)