Webi like it because it proves that kokushibo didn't hate yoriichi as much as he liked to tell himself he did.
He kept lying to himself to soften the pain, but he really did love his.
Webdespite the monstrous jealousy he harbored towards yoriichi, michikatsu still held a complex, deeply buried love for his younger brother.
This is heavily implied by the tears.
Webkokushibo absolutely still loved yoriichi, despite how much he tried convincing himself that he didn’t.
He lied to himself for centuries to soften the pain, but he genuinely still loved.
Webunfortunately yoriichi only had energy to deliver that one hit, he would've died even if he would've beheaded kokushibo.
Even after everything, yoriichi really thought highly of.