this story is about the demon king finding the reincarnation of the saint who killed him in his past life. in order to make her suffer he fucks her to make her fall in love with him and to be happy for once and right when she’s content he’ll make sure she lives in despair. but later on we find out that the two of them have been in love for decades and that all they want is to kill off everyone besides the two of them.
Tensei shitara Maou-sama ni Dekiai saremashita