Have they ever actually explained what the whole anti-sora form thing is all about? I always assumed it was a weird side effect from him being a heartless for a bit
Is anti-form originated from when Sora got turned into a Heartless? Nomura: Story-wise, yes. Drives are very strong so anti-form exists as a side-effect of using too much power. System-wise, I wanted to create something strong but troublesome.
...is what Nomura said in a 2006 interview.
iirc the fandom speculation is that since Anti-form happens if you use other drives too much. It might be that Sora "uses up" too much light at once and thus the darkness in him takes over for a moment, something along those lines. It's almost like Sora is more easily susceptible to the darkness after being turned into a heartless, and even Kairi's POH power couldn't remedy that.
With the appearance of Anti-Aqua in KH3 it also has the implication that Sora loses hope/succumbs to the darkness during a tough fight. And while we are on the KH3 topic:
There's a form that appears called "Rage Form," which reminds us of the "Anti Form" from KH2. What is the setup behind that? Nomura: The forms in this title are very different from that of KH2, so we decided to change all the names. Rage does indeed have characteristics that are reminiscent of Anti, but it's basically a separate thing setup wise. Anti is based on Sora getting completely stained in darkness, but Rage doesn't go quite that far. It's based on him going into a rampage state, controlled by feelings of anger.
from a 2019 interview.
Interesting that even though Sora has a shorter fuse and is angrier in KH2 (idr if it has been confirmed or if it's fanon speculation that it's due to Roxas in his heart influencing him and his heart remembering the pain and anger of CoM), it is only in KH3 where he is shouldering so much he snaps into a literal rage, specifically if he is damaged enough. He doesn't lose hope (yet), he gets pissed.
Considering the implications that there could be a part of Vanitas still in Sora it is currently hard to say if that rage stems purely from him or if Vanitas is feeding into it in some way.
It is actually one of the things I am hoping for the most in KH4. The build up has been going on for a long time, both through these forms and through his companions saying hurtful things to Sora repeatedly (it's often in a playful manner but that doesn't mean...it isn't mean. And KH3 really hammers this home.) and Sora's "Without my friends, I am nothing." may have scratched the surface but there's so much more to it.
Sora has a lot of pent up hurt inside him, Aqua being a direct parallel ingame. Aqua eventually succumbed to it because she was alone for so long. And now... Sora is alone, possibly missing memories or heart connections he needs to hold himself together. Yeah Strelitzia is there but that might not be enough. But let's stop here I could go on for hours.
