Marriage Toxin manga volume 5 features story by Joumyaku and art by Mizuki Yoda.

Gero swore to protect Hamster Master Arashiyama, but she's been kidnapped by the Beast Master! Now, Gero must team up with none other than Piichi the Hit Man Hunter to help rescue her. But the Beast Master is two steps ahead - have they been playing into his hands this whole time? And what does the unexpected return of Water Master Ushio mean for Gero?!

Includes the bonus one-shot “Hyper Hard Special Mission,” an exciting prequel story featuring Piichi and his girlfriend, Marin!