The oni clans have no distinct ties to Orochi, the way the other demons here do. I suspect many would have no interest in working with him.

[Some of them may be assholes, but Sen? Amagiri? He can't see them doing anything of the sort, and if they have the influence to keep their clans out of it...well, not that he knows much about their politics, but.]

They are dangerous opponents, but I do not think they have to be opponents.