I think it's the only way! One of these scenarios need to happen, or otherwise Caius will always have to hold back for Kouichi's intestines' sake!
The way you mention the latter I—
I'm personally rooting for some immortal and flexible organs so we can see some tummy bulge
I'm personally rooting for some immortal and flexible organs so we can see some tummy bulge love me some deep penetration
What will happen I wonder? Will Caius' dick be shrinked? Will he be shrinked as a whole? Or maybe Koichis ass will be magically transformed into a dimentional vortex of pleasure where everything fits and nothing gets hurt... Probably that one (▰˘◡˘▰)