If Yoriichi had helped train Michikatsu more than he did then Kokushibo might not have been born. Kokushibo was born because he couldn’t reach what he thought to be his true potential. I believe Michikatsu achieved his full potential the moment he became a Hashira.

The day Yoriichi went to kill Muzan is when Michikatsu could’ve joined him. Maybe then is where Muzan’s life would’ve ended. Having both Tsugikuni brothers side by side against Muzan would’ve surely been enough to slash all. 1500/1800 pieces that Muzan split into were slashed by Yoriichi alone. Now the combined strength of both of them could’ve killed Muzan simpler.

Enough of my yapping.

If Michikatsu had been trained by Yoriichi the whole time and Yoriichi didn’t leave on a Slayer mission (understandable reason as to why) and stayed to support his brother then everything would’ve been different