>>281960069
It's Zoro using all his haki powers without fear of death, and advanced CoC. Basically he couldn't cut King despite just scarring Kaido, was losing to Oden's sword, had an inner monologue that using all his haki powers would kill him. Then manned the fuck up and dumped it all anyways and that said if he wanted to fulfill his promise to Luffy and Kuina he should do at least that much; after dumping he got coated in aura and gained control of the sword, and knocked out people nearby proving it's conquerors. And the haki goes from Oden's color to Zoro's.

Essentially he's going haki Kaio-ken. It's just a powerup and aura bullshit.