A Sister Trope of Start of Darkness that involves a non-badass normal taking numerous levels in badass, whether instantly or over the course of a story, thus becoming essentially nothing but a giant walking, talking bucket of Nightmare Fuel.
Through a series of unlikely coincidences, or through accidental or unknowing actions on the part of the heroes themselves, or as a result of things which should never have happened — and in most alternate timelines don't happen, but just barely by the skin of their teeth, do happen — someone who might have stayed an insignificant nothing is transformed into a nightmare that grows and grows, absorbing the power to rend civilizations to dust and bring universes to their knees.
For some reason, it seems that From Nobody To Nightmare villains are always more powerful, terrifying, deadly, and threatening than your typical Diabolical Mastermind. In scenarios where the villain rose by their own effort, this often a case of I Did What I Had to Do, Jumping Off the Slippery Slope, and maybe a few Angst Nukes thrown in for good measure. This may owe itself to the shock value of the idea that anyone and anything can become the Big Bad under the right circumstances; it's much more comforting to believe that only long years of Card Carrying Villainy could possibly breed that kind of person.
Compare the Diabolus ex Nihilo. If the character was already a bad guy previously but never a serious one, it's Not-So-Harmless Villain. Heroic versions may still find themselves wondering, "Dude, Where's My Respect?". (Or becoming He Who Fights Monsters.) Frequently, the details of this process are uncovered in the villain's Start of Darkness. Contrast From Zero to Hero. Also see Who's Laughing Now?, Malignant Plot Tumor, and Magikarp Power.
Note that being a villain is not necessarily a requirement for this trope, even though most who fit the trope are. Anyone who is feared or dreaded by someone (even if the "someone" in question is the cruel and tyrannical government that the heroes oppose) can qualify. In such a case, the inverse trope is Villain Decay.
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- Western Animation
- Clamavi de Profundis: Oshrjad Bonebreaker began life as a stunted, abandoned orphan, but eventually grew to be a feared and powerful warlord leading a great orcish horde.
- Evillious Chronicles: Duke Venomania, otherwise known as Cherubim, as expanded in The Lunacy Of Duke Venomania, the tie-in to the song of the same name. He's a deformed guy who was locked in the basement because of this, and only two people actually cared about him...and then the girl he loved rejected him. So he murdered his entire family, made a Deal with the Devil, and raped pretty much every character in that story arc. Not to mention all of the murders and brainwashing he committed to keep it quiet.
- "The Lambton Worm": The Worm starts out as a tiny, harmless fish caught by John Lambton while fishing, small enough to be handled with ease and casually tossed down a well. The Worm then spends years growing within the well, and by the time it crawls back out it's a huge, powerful, terrifying monster that can hold all of the countryside in terrified thrall.
- In Wagner's Ring Cycle, Alberich is just a lovesick dwarf until he gets hold of the Rheingold and makes a ring which makes him a threat to the gods themselves.
- Dawn of a New Age: Oldport Blues:
- Simon in the present is a regular boy with an evil personality that's satisfied with cruel but petty crime. Flashforwards have shown that Simon becomes the head of an FBI division dedicated to capturing and persecuting superheroes, while the Dark Dragon moniker is formed into an evil organisation that kidnaps and tortures the superpowered kids.
- Barbra, a perfectly average girl in the present, is implied in flashforwards to have mutated into a horrifying monster as a result of her Adaptive Ability.
- Two minor examples are Eddie, a chill workman-cum-drug-dealer, and Esther, a kindly investigate journalist. Both are shown in the future to work as lackeys for the Post-Human Division and are set on detaining the superpowered characters.
- Frequently used in The Gungan Council for villains. Better examples would be characters that managed to fly under the radar for a year or two before everyone realized how nightmarishly involved they were in all of the galaxy's problems.
- Survival of the Fittest provides plenty of opportunities for (mostly) normal high school students to become multiple murderers. J. R. Rizzolo, in particular, went from being a regular guy who liked playing Guitar Hero to a sadistic, deceptive loony who offed his former classmates without a trace of guilt.
- Heather Duke from Heathers starts out as a Beta Bitch consistently silenced by Alpha Bitch Heather Chandler, and appeared rather meek compared to the person protagonist Veronica refers to as a "mythic bitch." When describing Heather Duke, Veronica even comments about how she seems to have no discernible personality in comparison to the other Heathers. However, after Heather Chandler's death, Heather Duke takes over as the new Big Bad of the school and is arguably even worse despite lacking the charisma to strike other students with the same feeling of fear that Heather Chandler did. She goes so far as to spread false rumors in order to completely smear Veronica's virtuous reputation, where as Heather Chandler had merely threatened her with social isolation.
- Ace Attorney:
- Joe Darke was an ordinary office worker, until he killed someone with his car. This led to a chain of events that made him an infamous Serial Killer.
- Phoenix Wright: Ace Attorney: The beginning has Miles Edgeworth. He's known as the Demon Prosecutor who is said to do whatever it takes to get his guilty verdict, including forging evidence (though Case 1-5 verifies that particular rumor was untrue) and who never lost a case before going up against Phoenix. It's later revealed though that Edgeworth used to be a perfectly normal kid, albeit one very interested in being a famous defense attorney. Character Development in later games makes him less of a nightmare, though.
- A heroic example to any of his opponents is Phoenix Wright. Phoenix was actually an art major in college when he decided to change careers and start studying law. By the time of the fourth and fifth games, he is known as a Living Legend and a respected figure in his field (though he still has his moments of being a Butt-Monkey).
- Danganronpa 2: Goodbye Despair:
- The students of Hope's Peak Academy's 77th class (excluding Chiaki) were all fairly normal, if somewhat messed up, high school students before they became members of Ultimate Despair. Afterward, they were responsible for the murders of their families and friends, terrorism, coup d'etats, wars, the massacre of countless innocents, and even destroying their own bodies through self-inflicted mutilation. The finale anime describes them as million-class murderers.
- Hajime Hinata takes the cake among the cast, starting off from someone with no talent being selected by Hope's Peak for an experiment. Said experiment erased his memories and personality to make him multi-talented for the sake of creating Ultimate Hope... but the aftereffects made him a prime target to become the Ultimate Despair, triggering The End of the World as We Know It.
- Discussed with Dennis in Double Homework. According to Marco, Dennis used to be a quiet kid who fixed everyone’s computers for free. However, this might be a subversion considering some of his hobbies....
- Fate/stay night:
- Sakura Matou goes from the cute girl with a jerk brother who gets kicked out of all the routes early, never does anything important, Cannot Spit It Out and more Shrinking Violet traits to an all-powerful dark mage with the exact magic traits needed not only to be able to be the host of the (sort of) devil but also express its power. And also to keep her mind (to a certain extent). Oh, and she can eat Servants or corrupt them as she pleases, has an immense Healing Factor, and a bunch of other nifty moves. The one thing it doesn't do for her is improve her self image, causing her to believe that Rin (her sister) doesn't care about her (Rin's rather cold statements don't exactly help matters...), and to worry that Shirou might abandon her for Rin.
- Avenger/Angra Mainyu started off as just an ordinary, run-of-the-mill Mesopotamian villager. After being randomly picked to be a scapegoat for "all evils of the world", he ended up being summonable for the Holy Grail War, but even there he was still pathetic, being one of the weakest Servants imaginable. However his spirit then went inside the Grail where he made a wish to truly become the manifestation of evil for revenge on humanity, and that's the reason the Grail has been corrupted ever since.
- In Hatoful Boyfriend: Holiday Star, The King was once a depressed quail whose otherwise-uninteresting life was so horrible that he became a Well-Intentioned Extremist Eldritch Abomination in the afterlife; he refuses to let himself be reincarnated and creates a fake fairytale kingdom where he steals the souls of all visitors, forcing them to become part of his hive mind so that nobody in the kingdom disagrees or is reincarnated, and they "happily" stay in his false paradise forever.
- Higurashi: When They Cry: All the secondary antagonists/ironic members of the main set of True Companions.
- In Nine Hours, Nine Persons, Nine Doors, Akane goes from being a sweet little girl to masterminding a second Nonary Game to get revenge on the four men that caused her death, as well as to get Junpei to show her the solution to saving her life.