Marriage Toxin manga volume 1 features story by Joumyaku and art by Mizuki Yoda.

Poison Master Hikaru Gero is taking on his toughest assignment yet—getting married! Gero couldn't be more clueless when it comes to the art of dating, but thankfully, marriage swindler Mei Kinosaki knows everything there is to know about love. Together, this unlikely pair will do whatever it takes to get Gero hitched—even if they have to take on the entire criminal underworld in the process!

As a deadly assassin from the poison clan, Gero swears he'll never settle down—that is, until the family orders his sister to produce the poison clan's next heir. Refusing to let his sister abandon her chance at true love with her girlfriend, Gero desperately turns to marriage swindler Mei Kinosaki for relationship advice. Can Kinosaki turn this trained killer into a charming husband-to-be?