Just because an anime character has an ability doesn't mean that they'll keep it forever. Sometimes anime characters lose their powers.
Some anime characters who lose their powers are heroes, like Edward Elric from Fullmetal Alchemist: Brotherhood. He loses the ability to perform alchemy in order to get his limbs and his brother's whole body back from the Gate of Truth. But others, like Orochimaru from Naruto, are villains who lose their powers in the pursuit of evil. Sometimes the loss is permanent, sometimes it's temporary, but no matter what happens, it's always dramatic - except when it's Kotoura from Kotoura-san, whose temporary power loss is played for laughs.
Which characters who lost their abilities do you feel for the most? Be sure to vote them up!
After Edward Elric regains his limbs and his brother's body, he has to give up something of equal value in exchange. The toll he pays is his ability to use alchemy. While this does require him to give up an important part of his life and identity, Ed considers it a price worth paying. His life without alchemy is a satisfying one - he focuses instead on marrying Winry and making some adorable babies with her.
All Might isn't the only person to experience this fate in My Hero Academia, but he's definitely the most well known. After transferring his quirk, One For All, to Izuku Midoriya, his own ability to use it waned significantly. Essentially, he was coasting on the fumes of his former power. He does this because his severely injured body can only tolerate using the quirk for so much longer, and he wants to pass it onto someone else who can take up his hero mantle.
At first, he's able to assume his muscle form and use the immense strength that the quirk bestows for short periods of time. But after a final showdown with his nemesis All For One, that ability disappears forever. He retires completely from the hero game, and focuses solely on teaching.
Perhaps one of the most tragic conclusions to a battle in My Hero Academia, Mirio resolves to save Eri from Overhaul, even if it means losing his own quirk. After all those years of training and honing his skills, he made it to U.A. High School's Big Three, garnering the reputation of someone who could replace All Might as the symbol of peace. But as Overhaul's bullet heads towards Eri, he throws it all away, caring more for Eri's safety than himself. Mirio is the living embodiment of what it means to be a hero.
Aizen is one of the toughest enemies in the anime world, so it's no surprise that fighting him is going to require some major sacrifices. To this end, Ichigo Kurosaki uses an intense bankai technique called The Final Moon Fang Heaven-Piercer. Using this technique, he assumes an awesome-looking form that allows him to use Moonless Sky. Using Moonless Sky, he creates a massive blade of Reiatsu energy that severely damages anything that gets in its way - including a fully evolved Aizen, who is forced to assume a much weaker form.
Unfortunately for Ichigo, the cost of this attack is steep - he loses all of his Shinigami powers, and is rendered a normal human. While he does eventually get them back, this is a major setback.