Adam has been a frequent screw-up for years, and it's implied he drove his parents mad (and Chris by extension) with all his antics. He's now trying to put his life back together.
Chris was close with his brother but ended up leaving for college in England, and essentially neglecting their friendship. After realising what his brother was going through, he's now trying to make amends.
William Griffin of KateModern performed frequent dangerous medical experiments on unwitting girls on behalf of the Order, but then decides to try to bring the Order down.
In Metro City Chronicles, Penitente began his superhero career because his mother and brother were injured by gang rivals during his youth.
Cube: ...and he keeps ending up with Kaoru? Maybe if you sent him for more sports training- Gendo: NO! He's there too, and that just ends up with them both in the showers!
Some agents in the Protectors of the Plot Continuum are former badfic authors hoping to undo the damage they've done to the multiverse, or ex-DIS who returned to the PPC when given the chance.
Yanagi in Canvas 2 after stealing the main character's painting five years ago.
In Marvels RPG, Ant-Man created Ultron, Iron Cross is a former Nazi-Super Soldier and Synch accidentally burned down his school when his powers first manifested. All are trying to atone for their pasts to some degree.
In Red vs. Blue, Agent Washington, formerly of Project Freelancer, becomes this after working with the Meta against the Blood Gulch Crew. Exemplified when Locus tries to give him a Not So Different speech.
Washington: I know I used to be a real piece of shit, but at least I am trying to do something about it.
Whateley Universe: Several, most notably Eldritch. However, the most striking example is probably Unverziehen ('The Unforgiven'), a former Waffen SS officer who spent the time since the war trying to atone for German war crimes:
Unverziehen was an enigma to most people, the insanely potent warper had been a member of the combat arm of the German SS, and had not been privy to the war crimes of Auschwitz, Dachau, Sobibor and other places. The man and Caitlin [Eldritch, formerly Eric Mahren] shared something similar: guilt. He felt responsible for what his country did during the war, and though her crimes paled in comparison to what the Nazis had done during that war, the A-List hero, who still could not forgive himself, hadnt physically committed any of the crimes he bore the shame of.
In Worm, Bonesawi.e.Riley becomes one of these after having a Heel Realization during the time she spent out of Jack Slash's direct control.
Glaistig Uaine also becomes one at the end of the series, again with a Meaningful Rename to Valkyrie.