he has to go now to the fenix clan site if i'm not mistaken to get the phoenix blood, it's been so long but i think it's that part. I read ATG in the novel, not the manga.
author I think when kaido gets the legacy of the true dragon god or collects all heretic seeds maybe you can make his profound veins have the element of destruction after all I think it's his most compatible element instead of creation god you can make him a destruction god