
this is a dumb question but i understand that his feet are suspended slightly above the height of the bathtub and even with his hands bound behind his back cant he sit up a little? ╮( ̄▽ ̄)╭

I'm not sure but I think he already was doing that. He said that his abs starts to hurt so it was probably because he tried to raise above the water level!
kotaro is best boi~ (=・ω・=)