Chapter Text
The Basics
The main thing to keep in mind is the relationship between Cores and Stars, it’s like squares and rectangles, all Cores are Stars, not all Stars are Cores. So while yes, the sun could be a Core and whatnot, it’s likely not.
Each Core is aligned with a certain color spectrum and elemental spectrum, like blue and lightning+ice or red and fire+wind, this extends to everything and while some cores are capable of utilizing other spectrums of power, it is more difficult and less rewarding than if they used their own spectrum.
Absorption is the act of consuming the opponents Core and subsuming their power for your own, in game we can see the result of failed and successful absorptions from the NPC’s each time they either gain power or lose power in regards to if they won or lost the absorption match, and just because they initiated the absorption doesn’t mean that they win, they have to break the Core’s defense before they can actually absorb the enemy, for the most part of what we've seen if they fail then they experience spectrum backlash, in which their Core becomes unstable and changes rapidly, eventually it calms down and they obtain a new form.
A combative technique is both a physical thing and a magical/psychological thing, by activating your technique, you are basically declaring your hostile intent to anyone nearby, as such when one activates their combative technique, it typically results in most if not everyone nearby activating their own technique in retaliation.
Fusions are the case when two equally matched Cores manage to succeed and fail the absorption at the same time, such an event is rare but not unheard of, the result is a spectrum fusion, taking the powers of the previous Cores and essentially multiplying them together, resulting in a much more powerful Core with the abilities of both spectrums.
A Mutation is what happens when a core absorbs another without utilizing the Absorption technique, as such the either the opposing spectrums clash against each other and the stronger one wins out, in which it ends up as just another absorption, but if the spectrums are similar enough, or both Cores are of equal enough strength, then the Cores undergo a mutation, with power equal to that of even higher grade Fusion Cores like Summum, such things are fundamentally wrong and nearly every single Core in existence, would attempt to exterminate any instance of Mutations.
In my MHA/Worldless world, Quirk energy (or what allows Quirks to do their own thing) is the same as Spectrum energy (or what allows Core’s to do what is essentially magic), this means that almost every Quirk can be replicated with the right usage of Spectrum energy, a decent example would be Eraserhead’s Erasure quirk would be able to be replicated by proper application of Seal magic. This means that in theory, any and all Quirks have their Core counterpart, just as any and all Cores would have a Quirk counterpart.
Blue Core’s are essentially allergic to water due to their spectrums natural manifestation, as Core’s can only exist as part of the Spectrum and can then utilize their respective Spectrum energy, they also take on attributes of their Spectrum energy. Blue energy is loose and free flowing while Red energy is rigid and stable, as such when a Blue Core has their form agitated by excess heat or a dispersing force (say Red Core fire or wind), they have a harder time keeping their form intact, and while some Cores are more resilient to such forces than others, water is the ultimate dispersion force, and as such any significant entry into water of a sufficient amount or rate (such as a pool or heavy rainfall), will result in the dispersion of a Blue Cores form, to be reconstituted at a location that the Core itself deems safe.
This is it for now, ask your questions in the comments and I’ll answer them when I see them.