They still haven't addressed that part of the
deepest lore as of yet. The only things that the devs have revealed is that the halos are what make them all nearly bulletproof and, IIRC, we're the only ones that can see the unique halo designs – the rest of the students apparently only perceive each other's halos as being generic-looking.
Story itself really wants to hint that some students may, in fact, be mythological deities/entities of some sort, given how it's been directly stated by this point that Shiroko's "true form" is Anubis and Hoshino is Horus. Kazusa has also repeatedly been referred to as "Cath Palug", which has mostly been played up as a joke, but who knows when it comes to the more nebulous portions of this game's lore.
Isn't a stupid korean thing about being half-robots, too?
Only one character is sort of a robot, and that's Aris.
(Related to the previous note, the game lore also directly states she's a product of some other nebulous group of entities called the "Nameless Gods", which are treated like some mysterious collective of potentially Lovecraftian, genocidal horrors alongside the group that worships them.)
It's insane how she was posted all over the place online, and then you actually play the game and get her and she winds up being a regular ranked character who's special is that she dodges attacks.
Regular Asuna, yes. Bunny Asuna is still definitely an SSR, alongside Bunny Karin.
The problem is, they're both dogshit in gameplay and nobody outside of delusional coomers would waste their time rolling on their reruns. Really, the crazier thing is that people conflated Asuna and Karin having bunny alts with them being best friends or whatever when the only real thread of connection between them is that they're just in the same group. Asuna and Karin hardly have much to do with each other otherwise, and I believe it's directly stated in-game that Asuna's really only in C&C because Neru is her best friend.
the only way to kill a character is by crushing their halo
Right, but halos can't be broken by just any means. Hell, they go over in Volume 3 that the methodology for "breaking" a halo really just involves subjecting the student to a sufficient degree of fatal injury that the halo can't sustain – or, in other words, torturing them to death or, as attempted in that very volume, setting off a sufficiently destructive bomb on them. Drowning/suffocation was also mentioned as an effective method.
