At first I really wasn't sure what I was looking at. Then I realized, 'That's a Dick' and a fucking huge one at that. Oh Japan, never change, for you must continue on with your destiny of enriching so many strange and niche fetishes.
It's interesting how Piyo draws girls more proportionately in this manga than most of his recent CG sets. Maybe at a later point, he figured, "They definitely like a phatt ass to go with a fat dick".