I mean, you also got Borgius who survived for however long after Crimson got booted out of his King seat, so maybe Crimson still held the title Monarch despite his treacherous act
Or that 13th class rando was there fighting before Arti got rotisserie’d
Pretty sure you were stuck with only Musashi + your own setup with that one
Honesly, the Shimousa boss fights were the biggest skill check of the game lol. They basically denied you the easy way out of just borrowing whales' support
Crimson's goal wasn't to get rid of that world of magic or something, but more like trying to usurp the Dragon God and become one himself, as Nebulim said
The Dragon kings need to die to advance his goal since the dragon kings are deathly loyal to the Dragon God, except Gilzea, king of Claws I...
I have my theory here is that it's because of that Thunder Claw he's using. He's only joined for a day so it's still too early for him to be given a personal Demonic sword, so that must be Kamui's and somehow it managed to save his life I guess