If Zoro joins against Kaido which is very likely, I see him injuring Kaido but not able to leave a permanent scar like Oden.
Luffy will definetly be the one to give the cou de grace to Kaido. He's the MC afterall.
Kaido
VS
Luffy (main character) zoro (enma) 6 scabards + izo (wano hero)
Big Mom
VS
Marco (met BM outside) Jinbe (help marco friend) nicorobin (help jimbe) sanji (big mom arc revenge & help robin) kid (want to kill yonko) killer (help kid) law (help jinbe and SH)
King
VS zoro (to allow luffy go up, then help luffy vs kaido)
Queen
VS kid (prison revenge, then join fight big mom)
Jack
VS neko & inu (ongoing zou revenge fight)
Perospero
VS sanji (vinsmoke revenge, then join fight big mom)
Who's who
VS xdrake (revenge)
Sasaki
VS killer Maybe? ideally denjiro in the roof
Black maria
VS yamato (cool girl fight as black maria seduce his dad)
Ulti
VS nami carrot shinobu trio (cheerful girl fight)
Page one
VS Franky Brook usopp chopper (fun squad fight)
Apoo
VS Hawkins (former kid apoo hawkins alliance betrayal revenge)
Fukurokuju
VS hyogoro (bad relationship since oden boiled)
Hotei
VS yakuza leaders (new samurai rulers vs old samurai rulers)
Since yamato & x drake switch side (not sure about hawkins)..
Seems all the characters to do the war & fights already there now..