The Last Witch is Bad Luck Charm

A world where technology has developed and people have eliminated fantasy and no longer seek stories. A boy named Saigo, who writes fantasy novels, is treated as a weirdo by those around him and is isolated at school. One day, a boy named Maori appears before Saigo, claiming to be the descendant of a witch and his destined partner. Suspicious of Maori, Saigo rejects his proposal of marriage. However, when Maori loses his emotions and causes a supernatural phenomenon, Saigo, sensing danger, agrees to marry him.

This is a dark fantasy about a descendant of a witch and a boy who seeks something out of the ordinary.

(Source: Natalie, translated)