I guess you are right. If I am correct, when Senjurou sent a letter to Tanjirou, it said something about Yoriichi telling flame pillar about how to defeat Muzan. But after hearing Yoriichi, flame pillar backed off. May be one has to die to unlock some potential for DOFG 13th step.
That hilt looks like hilt of the sword which was inside Yoriichi Zeroshiki. In chapter 104, the hilt of that sword looks similar to the spoiler shown here.
