[@jynmi88]
With armament haki, nothing says the regular, invisible willpower "armor" is particularly hard to apply to the whole body. But that's base level. What isn't regularly done is the more powerful hardening, where they turn black. Only Vergo and Pica, particularly powerful pirates, have been seen to do that to full body extent and their thing was being physically overwhelming.

As for Geppo, your explanation for it doesn't work. Geppo is specifically kicking/hopping off the air (or water) to float and propel the user, you know, like kung fu movies. It translates to "moon walk". Bouncing your limbs also doesn't really add any striking power. Even if it's some magical Sonic The Hedgehog unstoppable trampoline bounce, you're actively ruining your form by exerting force in one direction only to then exert yourself to push it the opposite way. That's not the same as just rearing back to throw harder.

Fortunately for you, a real, effective way to increase striking power is to push your bodyweight into the blow. It's why many knockout punches are accompanied by a small step towards the target or why hooks and kicks twist the waist and pivot the feet, you are putting your weight into a collision. You know what's really helpful for that? Being able to push off of air with your feet to send your entire body hurtling towards a target. Which is done in canon, see: Tekkai Sai. Just be very good at Tekkai Sai.

[@Red Alice]
Also hello, I'm interested. But don't hold the game back on my account, you start when you planned to and I'll find a way to insert my guy into the game when I get a CS done. Which may or may not take me days, mind.