Board Thread:Naruto Discussions/@comment-32617252-20180630010918/@comment-734582-20180701084830

Shadowclones aren't self-sustaining entities. Souls have little to no power to interact with the real world (see: hagoromo), yet Biju (if they're souls + chakra) can do so easily. Neither is chakra-like.

Besides, if a Biju is just chakra + a soul, then Yang kurama cannot exist. Kurama's soul was ripped out by Minato, and we know it was done in it's entirety because we've seen what cutting part of a soul looks like, and that wasn't done. Yin Kurama is chakra + Kurama's soul, but then Yang Kurama is still an entity of it's own. If that's just a physical body, then why does Yin Kurama also have a physical body?

Clearly, there's more to Biju than just Chakra.