I think Xebec dying and being completely erased from the world, his existence wiped out has led to Kaido's depression. Kaido may have really looked up to him and or Shiki too, given how kinda similar Shiki is to Kaido too imo.
There's that theme of men truly dying when they are forgotten, not just in physical/literal death and thats what happened to Xebec.
Kaido doesnt want that fate, he wants to go out gloriously and bravely like Whitebeard did, to be immortalised in history and by everyone for eternity, maybe even as a hero? Even people on the "villain side" or the "evil side" can have their own heroes too ofc!
There's been a lot of in-fighting and mistrust in the Rocks Pirates as been stated before, BM even said to Kaido not to trust the others or even Xebec too in that recent flashback panel and maybe the WG had a spy in Rocks or sowed some kind of distrust in them somehow through rumours, manipulation and such and led to them turning on each other too? Or they were just "too pirate" in nature for their own good, to function as a stable crew, too much "conqueror's/captain energy" or something? Lmao.
Kaido has given hints on why he's so depressed, he really hates humans, he is very cynical and says people will just betray you, humans cannot be trusted and are weak/inferior or so. He went berserk against Yamato briefly when she tried to reason with him and defend humans/Oden.
He was completely different when he met King despite thir circumstances and we dont know who Yamatos mother is, how Kaido met her and what happened to her. There might be some major tragedy there too knowing Oda and his actual open hatred towards mothers.
We also don't know why Kaido would work with someone as cowardly, two faced and pathetic as Orochi too, why did he even come to Wano, was he following Whitebeard who came there or for other personal reasons like to do with the One Piece or hearing about the samurai/Kozukis/Oden/Poneglyphs/Seastone or w/e? If Shiki was really associated with and even from Wano as suspected, that would explain a too! Oda implied Shiki is connected canonically with that witch transforming into him too.
I just wish Oda would stop fucking blue balling us on Kaidos past, motivations, why his character seems so incosistent due to all of this and such. We knew Big Moms backstory in WAY less time than this and its completely ridiculous! I believe WCI was only 87 chapters as I heard recently?! Quite a contrast by far...Wano is gonna be double that at this rate at least!
