By the way, in this chapter is mention Shimotsuki Ushimaru but what is even more interesting is that Onimaru VC mention the following:
<<according to Onimaru, Shimotsuki Ushimaru actually tried to oppose Kaido after Oden's death but died trying>>
Preview chapter we saw how similar Zoro is to Shimotsuki Ushimaru (and Ryuma).
If Ushimaru died directly against Kaido, that will have major impact for Zoro. Now facing Kaido is something much more personal for Zoro if he knew about that. And based how he reacted in chapter 997 by just seeing O-kiku arm falling in the sky, well his rage gona fuking explode.