Chotto dake Ai ga Omoi Dark Elf ga Isekai kara Oikaketekita

After defeating the Demon Lord in another world, Hinata Sunohara returns to Japan believing his life as a hero is finally over. One promise, however, did not remain behind: he had told the dark elf Mariabelle that he would marry her. Barely a month later, Mariabelle finds a way to Earth and appears in his room, determined to make good on that promise.

She moves in and decides that nothing will ever separate them again, using magic to protect Hinata and discourage anyone she considers a romantic threat. Between a modern world she barely understands and an affection intense enough to become possessive, Hinata's attempt to resume ordinary life proves harder than expected. Surviving another world was one thing; teaching Mariabelle that love does not require constant surveillance is another.