Oh sorry I meant Kouichi's ass is never going to be normal again haha
If Kouchi were to have been a Titan, then he'd be close to Caius in size. The first chapter shows us that, in the human world, Kouchi's pretty above average. He's tall, well-built, and has a big dick - dude's envy him, although he gets flustered. Caius, too, is also bigger than the average Titan. Kouchi briefly mentions this when he saw him sleeping - his feet were hanging off the end and the sheets were too short to cover him.
Both dudes are above their class of people, so it'd make sense that Kouchi would match pretty well with Caius should he have been a Titan. Or he could still be pretty small, there just wouldn't be much of a struggle fitting Caius inside of him.
If we think and not use yaoi logic isn't Kouichi tall in human standards? In the beginning of the story his friends were jealous of how tall he was and stuff. So if he's this short compared to titans then imagine if he were average height 0_0
Also I've like measured Caius's dick with my fingers and like you guys are right when you wonder how Kouichi's organs aren't rearranged lol his dick is big enough to reach Kouichi's upper chest/heart area when penetrating him 0_0. Kouichi's is never going to be normal so bless him for taking that dick.
Also I hope by some magic they'll have children together because they're a cute couple and that would be so adorable.