Itsuka no True End

Overview

"Marry me!" A world where the war between humans and demons has continued for hundreds or years... The hero was summoned from Earth to be humanity's ace in the hole. Aoi Yamato was a regular university student, but he led them to a sweeping victory and ended the war. However, the softhearted Yamato did not eradicate the demons, declaring that "the hero and the demon lord shall marry" as proof of peace. Fast forward to a year after their marriage... hero Yamato and demon lord Rei are enjoying a lovey-dovey, newlywed life. Yamato is madly in love with his gorgeous and devoted Rei... while the serious Rei tries his damndest to be a good wife in all capacities.

Source: AniList