Toilet Kids

One night, while visiting the bathroom, the protagonist suddenly finds himself flushed down the toilet and transported to a mysterious realm filled with strange monsters. Piloting a flying vehicle, the protagonist is tasked to defeat the the inhabitants of the mysterious world and find a way to return home.

Toilet Kids is an Japanese exclusive PC Engine vertical-scrolling shooter very similar in gameplay to Xevious. The game has only four stages and makes heavy use of toilet humor and scatological references.