Traumatic Superpower Awakening

When a character has latent powers or potential, there are three standard ways to unlock it: hit puberty, find a mentor to train them, or just have something really, really bad happen. Any form of trauma, physical or mental, can do the trick, but emotional blows are the most prevalent. The death of a loved one is especially common.

Severe trauma tends to release inhibitions that keep hidden potential in check. Strong emotions, most especially rage, work best. As such, the form of the awakening tends to be violent, even, in extreme cases, explosive.

With superpowers, once the bottle is opened, it can't be sealed again. The awakened one will typically need to seek training to control their new powers, so that their every emotional outburst won't trigger a new disaster. A period of How Do I Shot Web will follow, and learning to control one's emotions or face inner demons is typical.

This tends to coincide with Puberty Superpowers. Puberty is the most likely general time for powers to show themselves, but the specific incidence of the awakening will tend to be a traumatic one. There might be several minor uses of power, resulting from less serious emotional events, before the big push comes that makes the character fully aware of their potential.

Not to be confused with Die or Fly, in which superpowers awaken in response to a life-threatening situation, as a manifestation of a self-preservation instinct. See also Angst Nuke and Came Back Strong, which are very extreme variations on this. If the superpowers attained are related to the cause of the trauma, it's an Adaptive Ability.

Anime and Manga

 * Haku from Naruto discovered the full extent of his powers when his father tried to kill him.
 * This is typical for the sharingan. While the first form may also activate in Die or Fly situations, the advanced "Mangekyou" version requires severe trauma, so severe in fact, that the most reliable way to awaken was considered to be murdering your best friend.
 * Nagato got his Rinnegan when he saw his parents die (when they were stupid enough to act aggressively against soldiers). There might be more to it than that, as Tobi (a known liar) says he gave Nagato his Rinnegan. Whether this means he at least partly engineered the situation, did something else, or if it is just another lie, is completely unknown.
 * In Dragon Ball Z, Goku was able to reach the Super Saiyan Level when he saw Frieza Kill Krillin. Also, Gohan and Trunks from an alternate future obtained Super Saiyan this way (Gohan when the androids killed Piccolo, Trunks when they killed Gohan).
 * Elfen Lied: The protagonist was bullied by children and when they killed her dog, she killed them all with her unseen (until then) power of invisible arms.
 * In Inuyasha Kagome unwittingly uses the power of the magic Jewel of Four Souls which is inside her body to blast a demon which attacks her. Ultimately subverted, since the Jewel is released from her body almost immediately afterwards, meaning she no longer has that power. (Though this sequence of events does lead to her discovering and being trained in other latent powers.)
 * In Fairy Tail, a flashback shows Erza first using magic after seeing a friend die.
 * In Tiger and Bunny Lunatic's power manifested when he tried to stop his father from beating his mother.
 * Shiki in Tsukihime gains his Mystic Eyes of Death Perception as a result of his near death experience as a child.

Comic Books

 * This is common, though not universal, in X-Men. Puberty Superpower is more widely applied.
 * Jean Gray first used her powers when her friend got hit by a car and died in her arms.

Film

 * As mentioned above, the X Men movie franchise has many examples.
 * In the X Men First Class film, Magneto is originally only able to use his powers when extremely angry. The first two times, it involves maternal separation.
 * Likewise in X Men 1, Rogue first discovers her life draining abilities when she nearly kills her boyfriend.
 * Then there is Logan's awakening in X Men Origins Wolverine when he stabs his father's killer to death.
 * In the film version of Matilda, Matilda's telekinesis first displays itself when her father rips up her library books and tries to force her to watch TV with the rest of the family.
 * This happens to the main character in Kung Fu Hustle: after he is beaten to within an inch of his life, his chi flows are unblocked, and his potential to become the Greatest Kung Fu Master the World has Ever Known is suddenly realised.

Literature
Aldur invoked this for Belgarath by telling him to move a large boulder. When Belgarath became so frustrated that he shouted at the boulder to move, it did. Upon meeting another sorcerer in the Malloreon who gained his powers similarly, the main characters suppose this is the typical way for it to happen, and that it also explains why there are fewer and fewer sorcerers around, as the will of the universe prevents objects from being unmade: if someone, in a fit of anger, tries to unmake something, he will be himself unmade.
 * Garion of the Belgariad comes into his power this way. Though he is sensitive to sorcery for a while, and his first use of it is actually, unconsciously, to heal a brain-addled man, he first uses it intentionally against a man who has just slapped his Aunt Pol, and kills him when he learns the same man killed his parents. In the same way.
 * In one of the short stories in The Witcher book The Last Wish, a queen hires Geralt to kill a monster (actually a cursed prince) to stop him from marrying her daughter.
 * Harry Potter initially used his unfocused, underage magic in times of distress. This seems to be a common way for magic to appear in the setting, but not universal: contrast Voldemort, whose powers manifested as ways to manipulate and hurt people.
 * In The Wheel of Time, those who have the "spark", the more powerful manifestation of the ability to "channel", and who haven't been trained in channelling by someone who already can, will typically begin channelling unconsciously in their mid-to-late teens, and it will usually manifest itself during either a traumatic situation or when they wish to do something suitable for one who is angsty in general. For many, this takes the form of an eavesdropping weave or something similar. For one of the main characters, Nynaeve, it is an extreme sickness of a friend that leads to her unconsciously forming a healing weave.
 * In Sergey Lukyanenko's Labyrinth of Reflections, Divers most commonly acquire their rare gift under extremely stressful circumstances, such as when your friend is dying in Real Life and you have to exit Cyberspace right now without using any common devices.
 * In Mistborn, allomantic powers only manifest themselves following an intense trauma, which is usually a near-death experience (not always, though, as Kelsier, one of the main characters, came into his powers after watching his wife get beaten to death). Noble houses often severely beat their children to try and force "snapping".
 * Mercedes Lackey's Heralds of Valdemar The Last Herald-Mage has this. The protagonist, Vanyel, has his gifts triggered when his lover/soulmate commits suicide.
 * In Brightly Burning, Lavan's Firestarter gift was starting to come through as a normal Puberty Superpower, but being tortured by the older students snapped it on full-power.
 * In the orginal novel of Matilda her telekinesis first appears when she grows uncontrollably angry over being (loudly and violently) accused of something she did not do.

Live-Action TV

 * Angel, "Untouched". Bethany, the girl with telekenesis, had it awakened when she was abused physically and sexually by her father. It also flared up when someone threatened her in an alley early in the ep.
 * On The Finder, Walter's powers of deduction are purportedly because of a few bumps to the head that occurred during military service.

Tabletop Games

 * In the lore of Magic the Gathering, one in every million sentient beings in the Multiverse is born with a "spark", or the potential to become a Planeswalker. Igniting that spark and actually becoming a Planeswalker usually happens as a result of some kind of trauma or epiphany.

Video Games

 * Psycho Mantis of Metal Gear Solid had his powers fully awaken after he accidentally read his father's mind and thought his father would kill him, resulting in the destruction of his entire village.
 * Ryu in Breath of Fire IV gains the ability to transform into a dragon early on in the game, but for the first half of the game he only has access to his weakest form, Aura. It takes him seeing Captain Rasso massacre a village full of innocents (and forcing him to duel with a monster shortly afterwards) for him to unlock the much more powerful Kaiser transformation.
 * Rydia in Final Fantasy IV is an inversion; she has an innate talent for magic, but the trauma of watching her village being burned to the ground makes it difficult for her to use fire spells.
 * The premise of summoning a Persona in Persona 3 was that apparently, something traumatic has to have happened to you in order to summon it. MC was attacked by shadows. Junpei got the potential in a fetal position hiding from shadows. Fuuka's friend had to almost be eaten by shadows before she got hers. Mitsuru waas desperately trying to protect her father after seeing one of Kirijo's scientist turn into a shadow. It is unclear when Akihiko, Ken, and Yukari were found with the potential, but it might have had something to do with Akihiko's sister dying, Ken's parents dying, and Yukari's dad being in an exploding laboratory.
 * Lang in Legaia II: Duel Saga only awakens his origin, Galea, after being beaten to the point of near-death by a monster living at the top of Mt. Gabel.

Webcomics

 * In El Goonish Shive this is known as an Angst-Induced Awakening.
 * In Girl Genius this is typically how Sparks awaken.
 * Becka in Shadowgirls.
 * In Freak Angels it turns out that "near-death" experiences amplify the Freak Angels' powers and unlock new ones. For example, Arkady is capable of teleporting because of that drug overdose in her teens.

Western Animation

 * Parodied on South Park, when Cartman wakes up from coma due to a head injury, he fakes psychic powers in "Cartman's Incredible Gift".
 * A fairly mild example occurs in My Little Pony Friendship Is Magic. Young Twilight has to take an entrance examination to get into the School for Gifted Unicorns. She repeatedly fails the magic test which has been set up for her, leading her to become increasingly nervous, tense, and embarrassed. Then a large explosion occurs in the distance. Getting startled by the sudden noise when she is already strung tight as a wire triggers an enormous burst of random magic to burst from her horn.
 * In Avatar: The Last Airbender Aang is forced into the Avatar State when he is either in mortal danger or experiencing emotional trauma. A major focus of the story is him learning to control that power and to only use it when he wants to.