Power Loss Makes You Strong

A superpowered character finds himself without powers. Suddenly, saving the day is a hell of a lot harder. But he rises to the challenge, and succeeds. Usually gets his powers back at the end. This can serve to show that the hero is a hero for more reasons than just their powers, or at least that they are dangerous.

Compare Handicapped Badass, which is the loss not of a superpower, but of a normal human ability, Brought Down to Badass, in which the loss of a superpower does very little to hamper the character's fighting skill, and Disability Superpower, when the handicap itself ushers a superpower. Contrast With Great Power Comes Great Insanity. Inversion of Badass Abnormal.

Anime and Manga

 * Around chapter 120 of the manga, Code Breaker, you learn that
 * Accelerator in To Aru Majutsu no Index,  has his power limited to needing the calculations done externally and have them put into his brain via a choker looking contraption that only lasts 15 minutes. it gets upgraded, but the people who upgraded it installed a remote switch to turn off his power, so when he decides to save someone they want to kill, he just uses a pistol and wits to take out a group of hired delinquents (with Touma there helping out too, even if they both didn't know the other was there)

Comic Books

 * In the Justice League of America Elseworlds series JLA Act of God, a mysterious event wipes out all superpowers. Supergirl, Aquaman, the Martian Manhunter and The Flash re-train themselves to become Badass Normals like Batman.
 * Storm spent 3 real-world years powerless after accidentally getting shot by Forge with a power-neutralizing gun. However, she continued to lead the X-Men as a Badass Normal.
 * Literally, for Polaris when she lost her magnetic powers and gained super-strength for no clear reason.
 * The "Green Sun" story in Superman #155 (August 1962). Superman is not only rendered non-superpowered, but blind. He still manages to overcome the Big Bad using ingenuity and gumption.
 * The miniseries The Last Days of Animal Man depicts a near future where the middle-aged titular character, now a full time member of the Justice League, sees his powers slowly fade out to nothing. Nearly powerless, he finds a way to defeat two extremely Ax Crazy supervillains with sheer guts, resourcefulness, and the very last, tiny drop of superpowers he has left.
 * Blue Devil in the final arc of Shadowpact ... almost. He defeats a powerful demon without his own demon powers, but he does still have his original Powered Armor.

Live Action TV

 * Peter Petrelli from Heroes during the Villians Arc, and later after the Discard and Draw.
 * As often as Clark loses his powers on Smallville, this happens quite a bit, most notable being taking a bullet for Lois while weakened by kryptonite.
 * In the Season Nine opener "Savior", Clark is threatened by a woman with a katana while he is powerless, and he kicks her ass. In that season's finale, he does a fair job of holding his own against Zod himself in a brawl between the two where both are powerless. But he ultimately must make a Heroic Sacrifice in order to "win."
 * In the episode "Mortal", he takes out three baddies who had superpowers, albeit with the help of a flashbang and a sledgehammer.
 * Done on Buffy the Vampire Slayer when she turned 18 to see if she could function without powers, in the charming Watcher tradition known as the Cruciamentum. It was supposed to involve locking her in a house with an insane vampire. Then he broke free. Astonishing really, that most Slayers die young with that kind of a support system.
 * Actually somewhat of an Invoked Trope on the part of the Watcher's Council - if the Slayer could kill a vampire without her powers, then she would probably do a good job saving the world with them. If she couldn't, well... a new Slayer would be Called.
 * Fans have suggested an alternate explanation: slayers are called where they are most needed, and the Cruciamentum makes sure a slayer isn't only keeping one corner of the globe safe while allowing threats to grow elsewhere. Which leads to some Unfortunate Implications about the duties of a Watcher.
 * Another fan theory: once Slayers become adults they become even more powerful and may desire to survive independently of the Watchers Council, so the Cruciamentum is designed solely to kill Slayers after 18 so that they could keep future Slayers firmly under their thumb.

Literature

 * In Ghost Story, Harry is this.
 * In the Sword of Truth, Richard has one of these in the finale arc. It's just one of the countless call-backs to the first books.

Western Animation

 * Two in Justice League:
 * Superman in Hereafter, as he lands in a world with a red sun.
 * Green Lantern in The Savage Time. His ring runs out, there's no battery around, he becomes a rugged infantryman. To be fair, John is a US Marine veteran as well, so this is not exactly new.
 * One episode of Superman the Animated Series involved Canon Foreigner Luminus filtering out all but red sunlight from Metropolis. He proceeded to taunt, harass and play with Superman, knowing he was rapidly losing his strength. Oh, and he also mastered Hard Light by this episode, trapping Superman in a Western setting, Pirate setting and trying to run him over with a train. Superman manages to overcome this with good timing and playing off of Luminus's arrogance (seriously, Why Don't Ya Just Shoot Him?) until he can destroy the filtering device.
 * Ginormica in Monsters vs. Aliens after Gallaxhar strips her (no, not that) of her Applied Phlebotinum.
 * In the "Day of Black Sun" arc of Avatar: The Last Airbender, the firebenders lost all their powers. Princess Azula, being a very nimble individual, was still very effective. And having those Dai Li Earthbenders helped.
 * Her brother Zuko takes advantage the power loss to initiate his rebellion against their father, the Fire Lord. The Fire Lord, as is to be expected, is normally more powerful than Zuko, but he's no good at fighting without his powers. Zuko, on the other hand, is a master swordsman.
 * In the third season, Zuko experiences a hefty power loss once he begins to train Aang and figures out that his letting go of his anger and "Well Done, Son" Guy tendencies (and the frustration that brought him) has prevented him from using the The Dark Side version of Firebending the Fire Nation believes in. After a "life-changing field trip" with Aang he learns the "pure" form of Firebending and gets a dramatic enough increase in his abilities to successfully fight Azula one on one in the finale. Until she cheats, anyway.
 * The Sonic Sat AM episode Super Sonic involved Sonic losing his speed and saving the day without it.
 * Disney's version of Hercules. He killed a Cyclops without his Super Strength.
 * An episode of Batman Beyond featured Terry not only losing his technologically advanced batsuit, but having to face off against it when it's taken over by a rogue A.I.
 * He even lampshades the moment as defining character growth for himself, admitting to Bruce before the showdown that he needed to know whether he really had what it takes to be Batman personally, or if it was just the powers the suit gave him that made him a hero.
 * In The Longest Journey, April Ryan is able to slip between the worlds whenever she is threatened. By the time of Dreamfall, she has lost that power (due to fear, ironically) and had to become good at fighting to compensate. She partially gets her powers back, but not enough to use them reliably.
 * After Danny Phantom willingly gets rid of his powers to have a normal life again just when a giant asteroid threatens to smash the planet, he manages to come up with a way to save the world as well as comes up with a means to do it. Aside from that, he shows just how badass he can be without his powers, right before he gets them back.
 * Parodied, played with, subverted, and played STRAIGHT to Hell and back with Captain Atom in Batman the Brave And The Bold episode "Powerless".