Downplayed example in "Frozen Fever", a short sequel to Frozen that takes place on Anna's 19th birthday. Her sister Elsa wishes to make it the best day imaginable. Although Elsa was never evil, this effort is still partially driven by feelings of guilt Elsa has, mostly since their parents had their entire family isolated in an effort to protect Elsa for most of the sisters' childhoods, and Elsa has nearly killed Anna before, and once actually killed Anna by accident, although she came back to life. To help make up for all of this, Elsa wishes to make the birthday "perfect". However this is screwed up by her cold. Hilarity (and some Adult Fear) ensues.
Pterano from The Land Before Time VII: The Stone of Cold Fire becomes this at the climax when Ducky (who he and his minions had kidnapped earlier in the film) finds herself in grave danger—coincidentally, the same danger that got one of his believers killed during an earlier expedition for the Stone.
In Paranorman, the zombies, especially the Judge, aren't actually trying to attack people, but are trying to atone for sentencing a young and innocent girl to death as a witch.
Max Winters in TMNT, whose quest for immortality led to his generals, who were also his friends, becoming stone statues and unleashed a batch of horrific monsters on the world. In the present day he works with the Foot Clan to undo the damage to the world and friends and finally allow himself to die, even gathering his friends and being able to restore their free will so they can help. However, they don't see things the same way and like being indestructible, immortal powerhouses.
In the The Amazing Spider-Man, Peter originally interprets Uncle Ben's death as something he needs to atone for, ruthlessly hunting down the criminal responsible for killing him. It's not until he saves a bunch of people from falling to their deaths, specifically a small child, and realizes that the Lizard was Doctor Connors, that he shifts to acting more like an actual hero.
Ulfric in Black Death. As it is likely that he had been at the battle of Crecy, where their opponents had been slaughtered instead of being given a mercy strike. He does give one to the woman accused of being a witch.
In By the Sword, Suba is this by training himself back into Master Swordsman shape so that he can teach the helpless students, encourage good behaviors in them, and correct the Maestro's, Villard, behavior before he becomes just like him.
After Bobby is coerced to kill an innocent man, he breaks down until he confesses his crimes to his cop ex-girlfriend Beth and her superior.
After Eldon Perry gets his partner killed, he atones for his crimes at his promotion ceremony by exposing all the corruption taking place under Jack Van Meter inside the department.
Commissioner Gordon becomes this in The Dark Knight when he realizes Harvey Dent and The Joker were right about the extent of the corruption in his unit and, had he listened, it wouldn't have resulted in corrupt cops kidnapping Dent and Rachael, disfiguring the former and killing the latter. It only lasts until Two-Face kidnaps his family, but until then the sheer desperation in his voice shows how responsible he feels and how obsessed he is with rescuing Harvey:
Gordon: Dent is in there with them! We have to save Dent! I HAVE TO SAVE DENT!!!
Bruce Wayne/Batman is a big case of this. After behaving like a ruthless and careless vigilante, misjudging Superman badly, almost killing the Man of Steel and having an indirect part in his death in Batman v Superman: Dawn of Justice, he vows to form the Justice League to protect the Earth in Superman's absence, and does everything he can to accomplish this with the help of Diana/Wonder Woman in Justice League.
Suicide Squad: Diablo initially refused to use his powers, out of remorse for killing his family using them.
Arturo in Destroyer. He has spent the years since the robbery providing free legal advice to illegal immigrants. When Erin asks him if he thinks this will make up for his misdeeds, Arturo says that he cannot do enough to wash the sins from his soul, but that he will keep doing this until he dies.
In Dracula Untold, Vlad is portrayed as attempting to live a peaceful life with his family, and leave his days as Vlad the Impaler behind. Then the Ottomans arrive (again) and his attempts at a peaceful life become all for nought.
Sam turned himself in when he realised that one of his train robberies caused the death of 10 people. He was prepared to hang for his crimes, but when the alien invasion granted him an unexpected reprieve, he turned his skills to keeping as many people alive as possible.
Jules becomes this once he realises that it was his experiments with uranium that brought the Bugs to town. Abigail even tells him to stop feeling sorry for himself and find some way to redeem his miserable soul. Jules takes this advice to heart and spends the rest of the move trying to do just that.
In Jungle, Kevin—who had turned into a Jerkass during the Doomed Expedition—becomes this after he is rescued from the river. Recognizing that his actions were largely responsible for the accident that stranded Yossi in the jungle, Kevin does everything in his power to find Yossi: refusing to give up even when everyone else tells him that the search is helpless.
Imperator Furiosa from Mad Max: Fury Road states that trying to rescue the Wives from Immortan Joe is an attempt at redemption. We never learn exactly what she is attempting to redeem herself for, but given the highly savage and misogynistic culture of the Citadel, it's likely all the extra horrible things she probably had to do to attain the rank of Imperator.
Tony Stark, Natasha Romanov and Bruce Banner. Tony and Natasha have legitimate sins to make up for (he was a selfish weapons dealer who didn't care that the collateral damage from the military-industrial complex's freewheeling use of his weapons caused hundreds of civilian deaths; she was a cold-blooded Russian spy and assassin, presumably working for ex-KGB operatives, who also indiscriminately killed hundreds of people, including numerous civilians and, by implication, children). Bruce, however, involuntarily turns into a destructive, mindless monster when he gets angry due to an experiment gone wrong, and all the deaths he's caused happened when he wasn't in his right mind, but that doesn't stop him from blaming himself or even trying to kill himself to rid the world of the Hulk.
Also, Clint Barton became one after being freed from Loki's Brainwashed and Crazy mind control. In his case it's particularly noteworthy considering the only reason Loki enslaved him was due to his skill (making him a valuable pawn) and because he had 'heart', yet he still feels responsible despite having no control over himself. His first request upon being freed was to know exactly who and how many innocent people he killed while under Loki's thumb. Natasha shuts that down at once, telling him firmly not to think about the consequences of things he is obviously not responsible for.
In Thor: Ragnarok, Loki is guilty of various severe crimes outlined in the previous movie by his father, Odin. He later expresses regret and helps evacuate Asgard alongside his brother Thor, The Hulk, and Valkyrie from the rule of his and Thor's evil sister, Hela.
Skurge, a low level worker, takes the job of executioner for Hela and even leads her army against the heroes, but when Loki arrives on his ship, and it looks like the heroes are getting the upper hand, he blends in with the refugees and climbs aboard the ship. When Hela prevents the ship from taking off, he jumps out brandishing "Des" and "Troy" (two M-16s') and attacks her, and though he dies, he allows the ship enough time to take off and escape.
Captain Mendoza in the film The Mission used to be a cold-blooded officer who ordered the slaughter of many Guaraní natives, until he killed his brother in a fencing duel. He then went as far as climbing up a waterfall with a huge bag filled with Spanish armor tied to his back. Then he joined Father Gabriel and the Jesuits.
In Outlander, Kainan reveals that he had helped hunt the Moorwens to the brink of extinction, and that he considers his family's death Karmic Retribution. He doesn't have any qualms about killing the Moorwen that got loose in Norway, but he decides afterward to sever ties with his homeworld and stay with the Vikings.
Pain and Gain: Paul became one after his first stay in prison, and is very uncomfortable with the plan the whole time; the guilt actually seems to be what causes him to fall off the wagon and start doing cocaine again. He becomes one again when he's sent back to prison at the end. Ed even says he seems to embrace it.
Fry. At the beginning of the movie she tries to sacrifice her mostly civilian crew to save herself, despite the fact that her captain points out that the crew are supposed to put themselves last in crisis. At the climax, she tells Riddick that she would die for the others, and eventually loses her life saving Riddick.
Riddick might also count, as he appears to be ready to turn over a new leaf at the end, saying: "Tell them Riddick's dead. He died somewhere on that planet.".
In Purgatory, this describes everyone in the town of Refuge, though Lefty Slade fails.
Joshua Rose in Savior becomes this after being forced to realize that he's lost his humanity.
In Seven Swords, Fu's introduction proves him to be a heroic Old Master, and his sole purpose throughout is to save lives—which is hard for other characters to accept, having had personal experiences of him as an imperial executioner and torturer.
The work Lamont does as The Shadow is so he can atone for the suffering he caused as the ruthless drug lord Ying Ko.
Solomon Kane of Solomon Kane was once a savage and ruthless mercenary. After an encounter with a demon and learning of his potential damnation, he pursued first a path of pacifism to cleanse his soul and then a path of righteous battle to cleanse the world.
Stealing Heaven: After his castration, Abelard grows convinced he's been punished for the affair by God, thus becoming a monk as penance. He convinces Héloïse to become a nun as well, for the same reason, though she doesn't agree what they did is wrong.
In The Sunset Limited, Black is an ex-con who served his time for murder and found God, and now wants to help people.
McKellen: The Magneto that you see with me is a man of conscience, and a man with an unhappy life behind him. He's come through a great deal, and isn't taking on single-handedly, or even with the help of his Brotherhood, society as a whole. He's joined up again with his old friend, Professor X, and together, they're going to try to move things forward.
"He works in a steel factory, but he's not using his powers. I thought that was kind of interesting that he's doing honest manual labor. Penance is a bit extreme, but he's sort of left his world domination days behind him."
William Munny in Unforgiven really tries to be one of these; in his youth, he was a vicious, cold-blooded killer of an outlaw who only mended his ways when he married a saintly woman. After she dies, he struggles making a living as a hog farmer and trying to raise their two children until an old friend comes along to offer him a bounty on two cowboys who mutilated a young prostitute and went unpunished. When the trope is subverted and Munny's finally forced to come out of retirement, it's not pretty.