The creature chuckles, and as Genma watches his upper body shifts, changes. He loses the more monstrous features, and a moment later a blue-skinned man with a shark’s tail is hauling himself all the way up to sit on the bank, his tail still dangling in the water. “No one has to get hurt,” he says, and deliberately sets Genma's knife on the grass. “You unlocked my prison. I'm not going to eat the guy who helped me out.”

There's something in the water.