Merman in My Tub volume 5 features story and art by Itokichi.

A handsome merman named Wakasa is living with Tatsumi, a high school student - in his bathtub! Visits from Wakasa's crazy friends Takasu the octopus, Agari they shark, Mikuni the jellyfish, and Maki the snail raise the chaos level even higher. As if that isn't crazy enough, now a super-sadistic crab wants to take Wakasa away! The first meeting between Wakasa and Tatsumi is also revealed in this volume of the frothy bathtub comedy!