Manga by author 深海有光 - Status ongoing

A thousand-year-old monster and a human girl - their love travels across a millennium...She, who can see monsters, meets him, who has lived for a thousand years and longs for a quick death. He's the only one who can protect her, expelling monsters for her.A spiritual agreement reveals their entanglements from the previous life."Protecting you is the only reason that I live...'