Hello,
Now this is a topic that (to my knowledge) few people acknowledge/care about, and I understand why. Magic in KH often plays second fiddle to the classic attack button, which most people use especially on superbosses, which are immune to most spells anyways (reflect nonwithstanding). But the fact that magic is present in this universe means that, like any other fantasy game, it has rules associated with it (or at least, it tries to). For most games in the series, magic is leveled up from the most basic element to a -ra and then -ga level spell when the character gains a second level of it. In the original Kingdom Hearts, this can be seen as a good estimate on Sora's growing capabilities as a fighter, starting off with fire and growing to amass control over various elements and even time as the game progresses. Fittingly, he obtains the final fire upgrade before the final fight against Ansem making his journey come full circle.
But what am I really trying to talk about here? I want to understand how magic WORKS in KH
So there are a few ways that this happens in the series, and each seems to contradict each other. You've got games with MP bars (infinite magic provided you have MP left) which are in numbered titles as well as 0.2, deck commands (equippable magic with near infinite uses provided you wait for the command to refill) seen in Re:coded, DDD and BBS, and then what i call "item magic" from 358/2 days (finite magic that exists similar to a potion during a mission; once you use it, it's gone unless you use an ether, which you also have limited amounts of). But we don't know exactly what allows someone to use magic/makes it available.
Most people point to the "gargoyles" explanation of magic, where you need a conduit to channel it through, and you can't just use your bare hands or risk corruption. This can be seen in KH 1's Hollow Bastion, where Sora IS able to use magic through the wooden sword, but it's not as strong as it was when he used the keyblade. Other characters can use magic through other means, such as Ariel using potions or Merlin using his magic wand. Other characters might harness magic in different ways, such as Leon's fireball attack in KH 1 where he shoots it out of his hand. You might think that contradicts the theory, but it doesn't. Considering how KH is a blend of Disney fantasy and Final Fantasy RPG magic, it could be theorized that there are different styles of magic that can be learned. Perhaps because Leon was taught by someone in Radiant Garden how to cast a fireball before Maleficent took over, he can cast it through his hand, while Sora has been taught by Merlin and Yen Sid, Disney wizards who use conduits to cast magic. But KH 3 implies that even if you have a conduit, using high level spells can drain your energy, tiring you out. With this in mind, it can also explain how Sora is able to use -Ja and -za level spells in 3; he's grown enough to the point where he's able to use them, but he can't have it be a part of his arsenal whenever he wants, he has to work his way up to it.
So that's my attempt at understanding it. It might not be the OFFICIAL explanation, but given the mess that this series will become, it's the best I can do.
Now this is a topic that (to my knowledge) few people acknowledge/care about, and I understand why. Magic in KH often plays second fiddle to the classic attack button, which most people use especially on superbosses, which are immune to most spells anyways (reflect nonwithstanding). But the fact that magic is present in this universe means that, like any other fantasy game, it has rules associated with it (or at least, it tries to). For most games in the series, magic is leveled up from the most basic element to a -ra and then -ga level spell when the character gains a second level of it. In the original Kingdom Hearts, this can be seen as a good estimate on Sora's growing capabilities as a fighter, starting off with fire and growing to amass control over various elements and even time as the game progresses. Fittingly, he obtains the final fire upgrade before the final fight against Ansem making his journey come full circle.
But what am I really trying to talk about here? I want to understand how magic WORKS in KH
So there are a few ways that this happens in the series, and each seems to contradict each other. You've got games with MP bars (infinite magic provided you have MP left) which are in numbered titles as well as 0.2, deck commands (equippable magic with near infinite uses provided you wait for the command to refill) seen in Re:coded, DDD and BBS, and then what i call "item magic" from 358/2 days (finite magic that exists similar to a potion during a mission; once you use it, it's gone unless you use an ether, which you also have limited amounts of). But we don't know exactly what allows someone to use magic/makes it available.
Most people point to the "gargoyles" explanation of magic, where you need a conduit to channel it through, and you can't just use your bare hands or risk corruption. This can be seen in KH 1's Hollow Bastion, where Sora IS able to use magic through the wooden sword, but it's not as strong as it was when he used the keyblade. Other characters can use magic through other means, such as Ariel using potions or Merlin using his magic wand. Other characters might harness magic in different ways, such as Leon's fireball attack in KH 1 where he shoots it out of his hand. You might think that contradicts the theory, but it doesn't. Considering how KH is a blend of Disney fantasy and Final Fantasy RPG magic, it could be theorized that there are different styles of magic that can be learned. Perhaps because Leon was taught by someone in Radiant Garden how to cast a fireball before Maleficent took over, he can cast it through his hand, while Sora has been taught by Merlin and Yen Sid, Disney wizards who use conduits to cast magic. But KH 3 implies that even if you have a conduit, using high level spells can drain your energy, tiring you out. With this in mind, it can also explain how Sora is able to use -Ja and -za level spells in 3; he's grown enough to the point where he's able to use them, but he can't have it be a part of his arsenal whenever he wants, he has to work his way up to it.
So that's my attempt at understanding it. It might not be the OFFICIAL explanation, but given the mess that this series will become, it's the best I can do.