Crackpot theory: Where DID Ozma go to after we defeated it? Some giant voidsent with the power to swallow ENTIRE CITIES doesn't just poof out of existence just because we punched it a couple times (and filled it with arrows, and slashed at it, and... You get the point).
I think it's likely that it wasn't just a protector of the Nullstone, it swallowed something else that the Voidsent needs to revive Scathatch. If it didn't swallow Scathatch herself, or she didn't outright create Ozma in the first place. Would it have vomited out everything it swallowed somewhere?
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Also adding to the hopes that we see another Beast Tribe alliance quest. I especially want to follow up with the Ixal seeing as we've found their homeland. Not to mention Azys Lla is super barren as is, it's as if there's something else that's meant to be added there.