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When anime characters invent or discover a new technique, it's best to use that move repeatedly to keep getting those results. That's how action anime characters establish some of their most iconic moves, from Yusuke's Rei Gun to Deku's Full Cowl technique to Goku's unforgettable Kamehameha. Despite that, a few combat techniques were properly used a single time, and then never again.
It's easy to point out moves that were never repeated because the user was killed before they got a chance to use those techniques again, but that's a given. Of course, Kyojuro Rengoku won't use his best Flame Breathing moves after Akaza killed him, and Kimimaro Kaguya died before he could unleash his curse seal more than once. It's more intriguing to check out anime characters who used a cool move a single time without any repeats, sometimes because the character hasn't gotten a chance to fight again or is now permanently injured, precluding them from using those techniques any further.
Shinji's Bankai Is Cool But Too Situational to Use Often
The shikai and bankai found in Bleach are often used plenty of times, with Captain Byakuya Kuchiki being quite generous with his usage of Senbonzakura's release modes. Then there's Captain Shinji Hirako, a Visored and the reinstated Captain of squad 5, who's more conservative with his own zanpakuto. He has used Sakanade's shikai here and there, but only once did Shinji release his bankai.
In the Thousand-Year Blood War Arc, Shinji finally had a chance to properly use his weird bankai. With it, Shinji turned a squad of Quincy against each other as he twisted their sense of friend and foe, but Shinji hasn't done it again since. His bankai cannot be used if he has just one enemy, and it's unwise to use his bankai if he has allies around, so Shinji's bankai was limited to one use. Even when the Soul Reapers got desperate, Shinji's bankai was all but forgotten.
Water Luffy Was Only Effective Against Sir Crocodile
A number of anime techniques end up forgotten because they only work against a particular sort of foe, making them too situational for constant use. One Piece has one such technique called Water Luffy, which, at the time, was a fine example of how resourceful Luffy can be. It was also an early instance of One Piece characters finding a way to get around the incredible power of Logia-type Devil Fruits like the Sand-Sand Fruit.
Luffy's first fight against Sir Crocodile in the Alabasta Arc was a disaster, but the rematch played out slightly differently when Luffy brought a barrel of water to the fight. That didn't win him the match, but Water Luffy did give him a fighting chance, and it also saved his life when Crocodile tried once again to kill him. In the final showdown, meanwhile, Luffy used blood as a substitute for Water Luffy to strike his sandy foe.
Jogo's Domain Expansion Was Used Just Once, and Not Even Successfully
Domain expansion is often the ace in the hole for sorcerers and even some curses in Jujutsu Kaisen. It's designed as an ultimate move for any fighter, loosely modeled after the game-changing bankai releases found in Bleach, but Domain Expansion doesn't always work so well. No one knows that better than the volcanic curse Jogo, who used his own Domain Expansion just once — and not even fully.
Jogo tried in vain to release his volcano-themed Domain Expansion when he faced off against Satoru Gojo and Yuji Itadori, and he had every reason to feel confident. Then, Satoru used his power of Infinity to foil Jogo's Domain Expansion, which cost Jogo the fight. Since then, Jogo has not bothered to use his Domain Expansion all the way, and he didn't dare use it when facing Ryomen Sukuna, either.
Zero Hand Is Powerful But Requires Days of Meditation to Use
What makes the Nen combat system so delightful in the Hunter x Hunter anime is how it rewards creativity and off-beat thinking. Nen is rooted in the six main styles and can take forms ranging from smoke and lightning to gum-like material or even compounding interest, which helps set it apart from most power-based shonen systems. Just once, though, Isaac Netero defaulted to sheer power vs power as he used Zero Hand.
Hunter x Hunter fans won't soon forget Isaac's clash with the villain Netero, a fantastic example of the "tough old man" trope as Isaac lived up to his reputation among Hunters. After meditating for days on end, he released the Zero Hand move with his bodhisattva formation, but it didn't win him the fight against Meruem, unfortunately enough. Isaac hasn't tried this since, and Hunter x Hunter fans aren't exactly counting on it, either.
United States of Smash Was All Might's Farewell to One For All
It's true Deku used a loosely similar move called United States of World Smash in the third My Hero Academia movie, but that was a kick-based move with Full Cowl at 100%. Meanwhile, the original United States of Smash was a mega-punch that the symbol of peace All Might used in a miraculous moment. At the time, All Might was struggling to maintain his muscle form, and it seemed he could not take down All For One.
All Might scraped together the embers of One For All's remaining power in him, then combined it with his overwhelming willpower to go beyond to save the day. That may have been a cheesy and blunt way to turn the tide against All For One, but it worked, and it was a fine way for All Might to bid farewell to the power he had wielded for decades. It was also a cool culmination of all the Smashes named after American cities or states.
Vegeta's Final Crash Deserved a Bigger Spotlight
While the Dragon Ball franchise has a huge number of named moves that the heroes and villains use, they still tend to be used more than once each. This venerable shonen franchise never misses a chance for the characters to fight, so that provides ample opportunities to keep using moves like the Kamehameha or forms like Super Saiyan Blue. Still, Dragon Ball is home to a few moves the characters seem to have forgotten, such as the Final Crash.
This was a move Vegeta used against Reecome in the Namek Saga. Even by Dragon Ball Z's standards, it was a rather brutish and straightforward way to fight, and most importantly, it didn't work as intended. Reecome survived Final Crash's wrath with light injuries, and Vegeta has since moved on. Granted, Final Flash is rather similar to Final Crash, but it's stronger and is technically a different move, complete with a new name.
Dio Brando Didn't use His Ice Attack Again
Plenty of Stands are used repeatedly in JoJo's Bizarre Adventure, and a few non-Stand abilities or powers are repeated as well, such as Hamon. Then there's the matter of Dio Brando's moveset in Phantom Blood, including Dio's unusual ability to create ice in a fight. Dio used that move to put pressure on Jonathan Joestar in their main showdown, but it wasn't enough to spare Dio from total defeat.
Dio's ice move was not seen in use again in JoJo's Bizarre Adventure, seeing how Dio was reduced to a living severed head in Phantom Blood's final episode. Meanwhile, in the Stardust Crusaders ac, DIO was more interested in using The World, having either lost, forgotten about, or lost interest in his original non-Stand vampire powers. If fans really wanted to see more ice attacks, though, the avian Stand user Pet Shop delivered with the Horus Stand.
Rifles Are Surprisingly Effective Against Pure Titans, But They're Rarely Used
The combat system in Attack on Titan isn't always rooted in Titan Shifters pummeling each other, since the first handful of episodes didn't give the heroes very many Titan Shifter powers to use. Instead, soldiers like Armin Arlert had to make use of anything and everything they had, including rifles. Armin knew rifles could not take down Titans, but they could slow those giants down.
It was a truly unique and fun scene in Attack on Titan to see Armin's resourceful tactic come to life. As Armin planned, the soldiers opened fire with their rifles to blind the Titans, buying enough time for other soldiers to swoop in and slash the Titans on the napes of their necks. That was an outstanding tactic, but Attack on Titan's characters largely abandoned it in favor of later, stronger weapons such as Thunder Spears or even their own friendly Titan Shifters.
Roy's Left Hand Snaps Could Have Showed Up Again
Certain styles of alchemy and combat techniques are repeated often enough in Fullmetal Alchemist: Brotherhood, such as Greed's Ultimate Shield and Roy Mustang's fire-based alchemy with his right hand's finger snaps. Roy tended to use just his right hand, and during the Promised Day, he finally started using his left hand as well. With his left hand's snaps, Roy could vaporize the water in specific body parts, namely, eyeballs and tongues.
Roy used this move in just one fight as he tormented Envy with it, and after that, the left-hand snaps did not return. In one or two scenes, Roy had the potential to execute these pinpoint attacks, but then he was forced to perform human transmutation and lost his sight. From that point on, Roy had to use more conventional alchemy with hand claps, with no further mentions or usage of left-handed snaps.
