Evolved kappa. It only eats the flesh of obese men. It sits at the bottom of the sewer until an appropriate prey presents itself. It smiles when hit on the head.
Despite being the Water Tiger, this creature is Fire-based. That means that not only is Yuri's best fusion choice Man Dragon, but also that Margarete's Grenade does twice the damage it does to the regular Kappa. This battle is much easier than the enemy's HP denotes.