He did, yes.

"A few reasons. Valefor is not the best combatant for closed spaces like jungle clearings like this, most of her attacks are area attacks rather than concentrated ones and it would've been hard to coordinate with the three of you. But the main reason is that aeons can only exist in one place at a time—if I'm using Valefor, she will not be available for other summoners to use."

"—huh! So summoners just... share?"

"Mmhm. We can sort of—feel?—when we try to summon, if an aeon is available—but anyway they're best used as a last resort sort of thing, only when we really need them. If I call an aeon whenever I feel like it then someone else might have need of them and not be able to."

And all summoners are people who have been explicitly chosen by the fayth themselves to be the kind of people who won't do it frivolously. What an interesting system.

"Don't you have to train with them, though, to know best how they work and to have good tactical understanding of stuff?"

"Hmm, yes as far as that goes, but most of them have been around for hundreds of years and will just be much better than any given summoner at battlefield tactics. Most of what summoners and their guardians need to do is learn how to be what the aeons need, really."

"...huh. Can they speak?"

"Not in aeon form."

"So—how to be a game piece that plays well when the only clue you have about the overall game strategy is the behaviour of another piece."

"Yeah. Pretty much."

"But that still means you have to train sometimes."

"Yeah, sure, we just limit those times somewhat and let the aeons leave immediately if they feel a call elsewhere."

"—oh, they can do that. Okay. That makes sense."

"Sometimes I forget most people do not work as closely to the temples and summoners," Lulu pipes in, somewhat quietly, "and don't know the workings of these things as deeply as we do."

—oh, a ready-made excuse, thank you, Lulu, now he doesn't even need to come up with one.

"That makes me feel less bad for my ignorance."

"Don't."

"Never change, Lulu."

"I would not have anyway, but thank you for the endorsement," she replies dryly.

"So those spheres," says Azym, moving on to the next question. "How does that all... work? Where do they come from, why was one of them yellow?" If this is a very well-known thing he supposes he'll have to claim that he still hasn't recovered all of his memories but it feels like specific minutiae of combat that he's not necessarily going to be expected to know.

"...I should probably just have Kimahri give you a crash course in combat spheres."

"...hm."

"...later?"

"No. It is important."

The gist of it is that combat spheres are condensed power leftover from defeated fiends. Spheres in general are a natural way for pyreflies to arrange themselves in, whenever someone does the work to condense them at all, and the term "combat sphere" refers to those you extract from fiends when you use a certain special spell to do so.

By default, if you literally just grabbed a bunch of pyreflies from a dying fiend and condensed them into a sphere, you wouldn't have anything useful at the end, and you'd more likely than not end up accidentally grabbing the pieces of the souls of the dead instead, which no one wants. What this spell does is separate and order the dissipating pyreflies into useful pieces, defined sort of conceptually in intuitively straightforward ways. And more powerful fiends have more pyreflies tacked on in addition to the souls that make them up and so they typically can generate more combat spheres at the end. And then those combat spheres can get absorbed into your soul and expand your capabilities; that is the main way in which one becomes stronger.

However, you can't just graft spheres onto your soul without limit. It takes a while for the power to become truly yours, rather than borrowed or added on, and if you try to absorb too much all at once you'll end up just losing most of it; your soul won't be able to hold onto it without losing hold of itself and holding onto itself is its main job. The maximum amount of power you can safely absorb at a time is known as your "temporary maximum power", or informally "temp max". The best and quickest way to fully integrate spheres you've absorbed into yourself is through use. Typically, that just means combat, but it doesn't need to; you could in theory absorb a Power Sphere just as well by playing blitzball. It's just that eventually blitzball stops being a challenge in the right way, so you're not really meaningfully using any further improvements you get and so integrating them is slow. Fiends, on the other hand, can become unboundedly powerful, which makes combat always a good way to do it.

That spell is not, technically speaking, the only way to acquire combat spheres. You could make ones the same way you make any other spheres: gather up enough pyreflies, apply your will to them, the end. What that spell does, though, is make this process be very streamlined. Other ways of creating spheres require effort and care and thought; this spell makes use of the extant coherence of fiends, who are already solidified pyreflies themselves and who are already using those pyreflies for their own power, and just redirects that power. It's very efficient and effective, and creates a useful loop for field combatants.

As for the colour of the spheres, those are just built into the spell for ease of categorisation: red ones are standard spheres that improve you in one way or another, yellow ones are sympathetic ones that allow you to share power with someone else, and purple ones are extra-reinforced in a way that allows you to absorb them even if you're already at your temp max because they do the work of staying attached to your soul until fully integrated on their own. Which kinds of spheres a fiend drops is kind of complicatedly determined by the fiend's power and, in a manner of speaking, "personality", since all of magic is so emotions-based. Purple spheres are very rare, whereas red spheres are the most common.

That explanation gets broken up by fights with fiends but even though they're numerous and kind of stirred up by Sin they are not, individually, very strong, especially compared to their party. The main handicap they have is protecting the blitzballers, who don't have any kind of combat experience whatsoever. It's still not particularly difficult.

The temple they're going to is at the top of a hill that is not tall enough to be called a mountain. There are stairs leading up to it, some fifteen to twenty flights of them separated by circular landings, most of them reasonably small but one large enough to serve as a good rest stop with some benches and a great view of the village and the ocean, halfway up. But despite not being a mountain it is still very, very tall, and will require Rather A Lot Of Climbing.

"Damn," sighs Zei when they get there, having to shield his eyes from the sun with a hand as he looks up. "I don't suppose we could take our lunch break right here?"

"It'll be a lot harder to climb with a full stomach."

"Hey, hey," says Letty. "Fancy a race up?"