Talk:Nichirin Sword/@comment-46510030-20200801173701/@comment-44763576-20200817105947

I don't think so - the different Nichrin blade colours indicate the ideal breath style for the user, black blades being swords which are best suited for the Breath of the Sun.

I strongly suspect that the reason black blade users don't go far is because that when Muzan becomes aware of them, he has them actively hunted down & killed. Kokushibo claimed that he & Muzan killed all of the Breath of the Sun users, yet we know that Yoriichi couldn't successfully teach any of his students Breath of the Sun - that's why the various breathing styles exist to begin with. So either Yoriichi took on more students before he died & these students did learn Sun Breathing or the Breath of the Sun users Kokushibo speaks of were Demon Slayers with black blades who he & Muzan knew had the potential to use the Breath of the Sun (& who they killed before they could become truly dangerous).