At the climax of Kingdom Hearts 3 in the Keyblade Graveyard, Donald pulls out all the stops and surprises everyone (both in game and out) by casting the Zettaflare spell. This firmly cements Donald as one of the most powerful black mages in Square Enix history, but he isn't the only character to have cast this spell in the past. In fact, there are at least two other characters in the Square Enix cosmology that have been known to use this spell, making Donald the third and final caster so far to reach this level of absurd power.
For those less familiar with Final Fantasy spells, Flare is typically one of the ultimate spells in any given game, alongside Holy and Ultima. Ultima is the strongest of the three, while Holy is restricted to white mages and Flare is restricted to black mages. That said, there are more powerful versions of Flare, such as Megaflare, and Gigaflare, which are likely more powerful than Ultima but cannot be cast by the player and are typically exclusive to extremely powerful enemies. For Kingdom Hearts 3, Donald to cast Zettaflare means that the spell is stronger than Megaflare, Gigaflare, and even Terraflare by quite a bit.
Donald Duck's Zettaflare in Kingdom Hearts 3 (2019)
Donald Duck uses Zettaflare in a battle with Terra while the latter is possessed by Xehanort, lovingly referred to by fans as Terranort. At this point, Terranort has just decimated the entire cast of characters fighting for light and is about to deal what would likely be a finishing blow to both Sora and Kairi. Goofy interjects and deflects Terranort's attack, and while the villain is airborne, Donald begins to charge his mighty spell. It seems that only Goofy and Mickey know what this spell is, as both react with utter shock and urge Donald not to cast it.
Donald then unleashes the Zettaflare despite Goofy's protests and completely decimates Terranort, seemingly leaving nothing behind. This proves to be extremely taxing for the royal mage, as he then drops his staff and collapses to the floor motionless. It is later revealed that Terranort somehow survives the attack, but given that he is one of the strongest villains in the entire franchise, this isn't entirely surprising. Terranort has all of the knowledge and skills of both Terra and Xehanort with the added benefit of being in a youthful body, so for Donald to be able to defeat him is quite impressive.
Zettaflare in Bravely Default (2012)
Before Donald Duck, the second user to cast Zettaflare (although in this game it was localized as Zeta Flare) was the final boss of Bravely Default. This is a major spoiler for the entirety of the amazing game, Bravely Default, but at the end of Bravely Default, Agnes' Cryst Fairy companion, Airy, reveals that she was evil all along and has simply been guiding Agnes and the other warriors of light to do her bidding from the start.
The boss battle with Airy is incredibly difficult and takes place over three phases and in three forms. Though the first two forms see Airy take on grotesque and powerful shapes, her final form reverts back to a fairy like visage. In this form, her already formidable moveset is expanded with the addition of Zettaflare, the most powerful spell in Bravely Default and the entire Square Enix library at that. This is easily enough to instakill most characters, and will still severely wound even max level ones at that. She pairs this with her unique Acedia attack to overpower foes. With Bravely Default 2 on the way, maybe a fourth user will arrive.
Bahumut's Zettaflare in Final Fantasy 14 (2010)
The first ever use of Zettaflare, and perhaps the most appropriate demonstration of its power, came from Bahamut in Final Fantasy 14. Traditionally, Megaflare is Bahamut's signature attack, and Bahamut himself is usually the strongest summon in any given game, but in Final Fantasy 14, Bahamut goes beyond this. In the amazingly animated intro cutscene to Final Fantasy 14: A Realm Reborn, Bahamut breaks free of his bindings and casts Terraflare, which completely devastates the entirety of Eorzea, being later referred to as the calamity. It takes over five years for the people to rebuild after the destruction it caused.
Zettaflare is used by Bahamut in a special event version of his boss fight and is theoretically even more powerful than Terraflare. This is notable because the calamity that is Bahamut's Terraflare was the in game explanation for Final Fantasy 14's reboot as A Realm Reborn, meaning this technique literally killed a video game and forced it to reboot entirely. Keeping in mind that Zettaflare is theoretically several magnitudes stronger than the Terraflare seen here really puts Donald's feat in Kingdom Hearts 3 into perspective.
How Strong is Zettaflare?
Despite the fact that one of Zettaflare's users, Airy, was capable of completely destroying alternate realities that represented other players' games, there is a mathematical way to quantify Zettaflare's power. The naming convention of flare moves, using mega, giga, tera, etc. is directly correlated to binary prefixes used to describe things like harddrive space. A gigabyte is 1000 megabytes, and a terabyte is 1000 gigabytes, for example. Beyond terabytes, are petabytes, exabytes, and zetabytes, each being 1000 of the previous one. This means that the Zettaflare is the equivalent of one sextillion flares, which would be written out as a one followed by 21 zeros. When compared to the Terraflare which Bahamut used, it is 1 billion times stronger.
Naturally, this level of power is difficult to understand, as human brains simply can't fully comprehend such high numbers, but that just makes Donald's feat all the more impressive. Put plainly, Donald Duck cast the most powerful spell in Square Enix history, and to Terranort's credit, he was somehow able to survive it. That said, there is of course always artistic liberty involved, as if the power of these spells truly scaled in this way, nothing would be able to survive a simple Megaflare or Gigaflare, much less a Terraflare or even Zettaflare. Yet, enemies and player characters alike in Final Fantasy-esque games seem to whether these types of attacks time and time again.
Kingdom Hearts 3 is available now for PC, PS4, and Xbox One.