...

Uhhhh so like what I think what happened was that he really liked humans and wanted to help them but he became so corrupt over something that he practically turned into a monster, and he was killed, sorry if I’m wrong I’m also a lil confused

same i’m so confused

same here, but here's what I got:
Kayaya is the tiger divine beast that lived before Nuah and Kayaya was extremely fond of humans and loved living alongside them. Overtime, maybe this love he had for them forced him to do somethings(idk maybe overusing his powers or flying into a rage? since he loves humans so much, even a little injustice towards these humans he cares about would be magnified), that eventually corrupted him and caused a 'calamity' i dunno they showed people screaming and all, maybe he killed a lot of humans in the cross fire...?
the other divine beasts, aka banam etc, chose to kill Kayaya because Kayaya couldn't be brought back anymore, and during all this chaos Roymzu
wasn't present. And since Kayaya was a full divine beast with lots of power (unlike current Nuah), after Kayaya was killed maybe the power that seeped out was what poisoned the lands.
[I dunno man i tried-]

Thanks youuuu now everything has cleared up for me TvT No wonder Roymzu doesn't want Nuah to have anything to do with Rix