So sad he let his heart darkened with jealousy and hatred and also blinded by them towards his little twin brother. Even Yorichii has surpass him when it comes being a very skillful and powerful true swordman he has not even looking down on Kokoshibo, or mock him and saying some lowest stuff to him like:
"omg since you were a kid you were the only who was interested on swords where you were doing well and practicing but now look at me someone who didn't have interest of becoming a swordsman before I become more stronger and do better than you. You're literally nothing compared to my swords skill now"
Imagine, your brother always praise you, respect you and have you as someone he look up since he was kid to the fact you have to go to narrow path just beat or k!ll that brother. That's sad and heartbreaking.