Marriage Toxin is a Japanese manga series written by Joumyaku and illustrated by Mizuki Yoda. It follows Gero, an assassin from a long line of poison users, who is forced to enter the world of marriage to preserve his family line. To help him, he teams up with a skilled marriage swindler, and together they navigate dangerous missions, romance, and comedy. The series blends action, humor, and relationship drama in a modern shonen setting.