Just because a power exists doesn't mean that it's always a great idea to use it. In fact, some are so dangerous that they're straight-up forbidden - or at least, their users know to be extremely judicious about when they resort to them.
Some forbidden anime powers are banned for their hugely detrimental impact on the user. The Eight Inner Gates, a taijutsu technique from Naruto, almost inevitably results in the user's demise. Others have the potential to create mass casualties. The Athena Exclamation from Saint Seiya is the rough equivalent of the Big Bang.
Do you think that these moves are banned for good reason?
Human Transmutation - Fullmetal Alchemist: BrotherhoodPhoto: Studio Bone
Human Transmutation is explicitly banned in the world of FMA, and for good reason - it doesn't work, and the consequences of attempting it are dire. Multiple alchemists have tried to use Human Transformation to bring back a deceased person. When Ed and Al tried this with their mother, they not only failed to bring her back, Al lost his entire body and Ed lost an arm and a leg.
One potential benefit involves having the secrets of the universe forcibly stuffed into your brain when encountering Truth and the Gate, but that painful and terrifying process may not be worth the knowledge it brings.28020Banned for good reason?
Summoning: Impure World Reincarnation - NarutoPhoto: Studio Pierrot
This kinjutsu was banned by its creator and for good reason. It allows the user to bring a deceased person back to life and control their behavior. This is already gruesome enough, especially if the newly revived person is being forced to attack their allies against their will.
But it gets worse. This technique requires a human sacrifice, which means that anyone who uses it probably has to take a life, unless they happen to have a recently deceased body lying around. So it's both excessively violent and wildly disrespectful to both the sacrifice and the revived person.25520Banned for good reason?
Eight Inner Gates - NarutoPhoto: Studio Pierrot
This taijutsu move is enormously powerful, but it's usually the last thing its users ever do, which is why it's a kinjutsu. By opening 'gates,' or internal restrictions on the flow of chakra, the user is able to dramatically boost their strength. But anyone who opens all eight invariably destroys their body in the process.
The only reason Guy survived using this technique against Madara is that Naruto had just awakened some absolutely bonkers healing abilities of his own. Even with that, he still remained disabled for the rest of his life.25721Banned for good reason?
Wish Granting - Hunter x HunterPhoto: Madhouse
There are plenty of hyper dangerous moves in the Hunter x Hunter world, but this is one of the few that anyone other than the user tries to control.
Alluka Zoldyck is a little girl with no Nen abilities of her own, who is possessed by a being from the Dark Continent called Nanika. When a person fulfills three of Nanika's requests, she will grant a wish. The bigger the wish, the more difficult the next set of requests will be. Should a person be unable to fulfill Nanika's requests four times in a row, they and their loved ones will be brutally and instantly destroyed.
For this reason, Alluka's family keeps her locked in a safe compartment, and rarely allows the wish-granting powers to be used except on rare occasions. When Illumi believes that Killua is going to use it to help Gon, he immediately mobilizes to try and destroy his own sister, and is only stopped when Killua explains how he plans to circumvent the grave consequences.19224Banned for good reason?