Anime is home to some of the most amazing and creative superpowers ever seen in fiction. Whether these abilities mildly strengthened their user or turned them into a physical god, they almost always came with a price. Some powers had an understandably high exchange rate, while others demanded a price that was just unreasonable.
In exchange for often fleeting power and might, some characters willingly gave up parts of themselves or even all of their humanity, or were tricked into doing so. These were almost never worth it, and the lucky few didn't live to see the folly of their choices. The rest, unfortunately, lived long enough to witness their power's consequences.
Spoilers ahead.
10 Yomiko Readman's Papermaster (Read Or Die)
Read or Die's Papermasters had one of the most unique anime powers. Papermasters could telekinetically control paper and shape it into whatever form they wanted. Some Papermasters created constructs, while others turned stacks of paper into weapons. Yomiko could do these but at the cost of becoming a bibliomaniac.
Yomiko wasn't a bookworm; she was literally addicted to books. Yomiko's powers made her crave books no matter what. She spent tons of money on books and ignored basic health and hygiene to read more. Yomiko's addiction made it impossible for her to function in everyday life, and she would've died were it not for British Intelligence's help.
9 Dabi's BlueFlame (My Hero Academia)
Every Quirk in My Hero Academia has its strengths and drawbacks, but Dabi's BlueFlame is one of the most self-destructive. Dabi is arguably the anime's strongest pyrokinetic. BlueFlames was so hot and powerful that it even surpassed Endeavor's Hellflame. However, BlueFlame was so powerful that it burned Dabi alive.
Dabi barely survived, and he was forever changed. More than half of his body was burned, and it's been confirmed that his Quirk's flames could consume him if he pushed himself too hard. Dabi accepted this and is now determined to burn to death with his spinoff-worthy father, Endeavor. BlueFlame basically turned Dabi into a literal time bomb.
8 Blackbeard's Dark-Dark Fruit (One Piece)
Trading the ability to swim was a high but otherwise fair price for eating one of One Piece's many Devil Fruits. Even if this trade-off was detrimental to sailors and pirates, Devil Fruit users didn't really mind it since they became superhumans. Blackbeard, the pirate with the sixth-highest bounty, was the exception since his Dark-Dark Fruit made his life worse.
The Dark-Dark Fruit let Blackbeard control shadows and nullify or steal other Fruit users' powers. This was a uniquely evil power that also amplified the amount of pain he felt. His fruit also didn't enhance him physically the way other fruits did, and it robbed him of the ability to sleep. These turned Blackbeard into the miserable and shrewd pirate he is today.
7 Artificial & Natural Vampirification (Hellsing Ultimate)
Hellsing Ultimate's recurring theme was that immense supernatural power was not worth it. Being a monster like a vampire or a werewolf granted people eternal youth, immortality, and incredible powers. However, anyone who became a monster also threw their humanity away and doomed themselves to an eternity of loneliness.
The only times that the Last Battalion's lab-made Nazi vampires and even the powerful but dubious Alucard felt alive was when they threw themselves into life-or-death situations, like war, and when they brutalized others. Becoming an all-powerful monster denied these people any chance of normalcy and only made them yearn for death.
6 The Curse Devil's Sword (Chainsaw Man)
Anyone in Chainsaw Man who struck a deal with a devil basically doomed themselves to suffering in life and death. Through the Curse Devil, Aki Hayakawa could theoretically kill any enemy with just a few sword strikes and condemn them to eternal damnation. The price was that each blow cost years of Aki's life.
After using the Curse Devil's sword three times against Katana Man, Aki was informed that he only had two years left to live. To add insult to injury, Aki's attacks barely fazed Katana Man. Not only did the Curse Devil charge a steep price for renting its powers, but it was arguably not worth it since it was ineffective.
5 A Shinigami's Death Note (Death Note)
Death Note's eponymous notebook is one of the most famous fictional weapons ever conceived, but even its biggest fans tend to forget the high price it charges. In exchange for a fraction of a Shinigami's powers, a Death Note's user would automatically condemn themselves to a deathless afterlife in Limbo the moment they use it.
The Death Note had many rules and benefits that exacted equally high tolls. For example, using a Shinigami's Eyes (or seeing people's true names) cost half of the user's current lifespan. The Death Note's steepest price was a user's humanity, as seen in Light Yagami's descent into mass murder and delusions of godhood.
4 Piloting A Gundam (Mobile Suit Gundam: The Witch from Mercury)
In Mobile Suit Gundam, piloting a powerful Gundam was never easy. But in The Witch from Mercury, doing so could kill even the most skilled pilots. The GUND Format allowed pilots to synchronize with their Gundam, but doing so strained their bodies and caused immense pain. Reaching a high enough Permet Score was fatal.
The only way to survive was to be genetically modified the way Elan Ceres' body doubles were. Except for Suletta Mercury, pilots treated their skills as a curse. As exemplified by Sophie and Norea, shortening their lifespans and subjecting themselves to the horrors of war to pilot superweapons was a terrible trade.
3 Inheriting The Attack Titan (Attack On Titan)
Becoming a Titan was one of the worst things that could happen to anyone in Attack on Titan. This was true even for Titan Shifters, who retained their humanity and gained one of the nine Titans' powers. In exchange, they would die in 13 years. Those who inherited the Attack Titan got the most powerful Titan and paid the highest price.
The Attack Titan could transcend time and space. This granted the holder the ability to rewrite the past to change the future. However, this also meant that they experienced previous and future holders' misery all at once. This immense power made Eren Yeager's already difficult life even worse and completed his descent into evil.
2 Becoming A Magical Girl (Puella Magi Madoka Magica)
Puella Magi Madoka Magica became famous and even reshaped the entire magical girl anime with its dark take on a magical girl's powers. Here, ordinary girls could become magical girls by making a contract with an Incubator. In exchange for fantastical powers and becoming the hero of their dreams, these girls lost their humanity and future.
To wield their cosmic magic, a magical girl was transformed into a hollow shell whose soul was locked away in a gem. Given enough time and despair, magical girls were doomed to become the very Witches they fought. Worst of all, the Incubators didn't tell the girls about this because they only saw them as batteries to use and dispose of.
1 Becoming The Ultimate Weapon (Saikano)
Apparently, the only way to stop the endless wars in Saikano was to turn the innocent Chise into a living superweapon. Chise was Japan's trump card, and she was the most powerful person alive. Chise's might was so immense that she only became stronger with time. In fact, Saikano ended with her basically ending the world.
None of this was worth it since Chise's life was turned into a living hell. Being a weapon meant that every waking second was painful, and her mechanical transformations made it worse. By the end, Chise was nothing but a mass of sentient energy that was so consumed by suffering that she ended the world as a mercy kill.