Marriage Toxin manga volume 4 features story by Joumyaku and art by Mizuki Yoda.

Not long after accepting his latest assignment to protect Hamster Master Arashiyama, Gero is struck by a surprise attack from the deadly Hit Man Hunter! To make matters worse, Arashiyama's life is threatened by the head of the Beast Clan. Now, to have any hope of keeping her safe, Gero must risk venturing into the very heart of this rival clan's territory…