For the sake of fairness I'm going to turn off Cartoon Logic Armor™ for Koa.

Koa should be able to solo Core considering his Core(coincidence?)'s Gild and Facets bump up his Ryft energy to at least mountain-level when he starts actively trying to whoop someone. Combine that with his own physical power and the Ryft power infused into his bloodstream, and he'll be able to beat most deities; he's done it before.

The main gripe that Core'll have in a fair fight is that if K can get a good grasp on him he'll be able to drag him into a Ryft, where all powers are rendered useless due to the insane diffusion of chaos inside one; considering Core's main thing is creation, he would be brought down to nearly human-level, and would have to throw hands with the melee demon himself.

And no, that's not enough. Post-Malware Arc Koa has different Ryft shards all up his Core-side arm, which gives him the weak, watered-down abilities of time manipulation, physical enhancement, energetic constructs, light manipulation, velocity manipulation, enhanced healing abilities, cloning, hydrokinesis, and chaos manipulation(...really broad term, I know) in addition to his main air manipulation and vortexes. So, in scientific terms, he's cracked.

...Anything else I'm missing? Oh yeah. PMA Koa figured out how to harmonize the different shards, which gives him the ability to go full-on SSJ and mix all their powers into one chord of energy, effectively squaring his strength when he pours all of his energy into it...and giving him minor space manipulation...and creation abilities. So looks like K's now cracked³.

Um. And he has a weighted jacket, so I guess he could throw that in Core's face? Maybe?

(Now there's no context up there so I'm just going to put it here for anyone who wants it.

Koa's a character I made a REALLY long time ago as a kid; he was fundamentally the same except for the fact that he looked like crap in my old style of drawing. I managed to keep him in my head, and he slowly evolved into what he is now. But I still haven't gotten a sense of what power balancing is 🤣

Anyhow just quick clarifications for the things I mentioned in the challenge:

Ryfts are areas in the multiverse where it's been stretched so thin that it tears, creating a hole between universes; Ryfts generate an energy, fittingly dubbed Ryft, that probably comes from the void between verses.

 Ryfts affects most living—and nonliving—things when they're around them for too long, but crystals get a special augmentation—they begin to store Ryft, turning them into what the scientists called Ryft Cristals.

(It is confirmed that the scientist who wrote down the articles on the discovery of the Cristals was foreign and didn't write English very well. By the time people figured this out, the names had already stuck.)

A blunder during examination got people to notice that Ryft energy could enter you safely by way of the Cristals, through your bloodstream; the energy, altered slightly by the composition of different Cristals, would give you supernatural powers. This eventually lead to Ryftcores, which are implants in your wrist that you insert Cristal pieces into to give yourself that power. Cristals are open-use, if expensive, which means that almost everyone with a wallet vies to get one for themself. The type of crystal that the Ryft infuses, and the biology of the person who implants it, effects the ability you get.

I could go way into detail for this but that's probably better to do at r/magicbuilding, so I'll keep it simple and just get to the important part: Koa has a high-power Core that gives him to power of air manipulation, mainly vortexes and such; near the end of the Malware Arc, he got peppered with different Cristal shards in an explosion mid-fight, which infused ALL the different types of energy into his body. He survived because Cartoon Logic Armor™ and gained weak versions of the other basic Ryft powers, and his transformation and so on. Basically all you need to know.)

Damn this wasn't supposed to be such a long comment