Tasei's Kid is a water creature that can be found in the lake of Witch's Island. It has a single red eye and green snake-like body. There has 1/16 chance it will appear in the lake each time you enter the screen.
Like other water creatures, it cannot be reached and only reacts to the Cat effect. Interestingly, it has a sound effect set to play when interacted with even though it can't be reached, which seems to be Unused Content.