The appropriate costing of such a Catch, let alone whether such a Catch is appropriate in the first place, is a point of significant contention.  Tread carefully.

High Concept: Denarian Biker Seeking Redemption
Trouble: Slippery Slope
Aspects: I Can Do Bad By Myself; Mad Wrench Is Mad With A Wrench; Knowledge Of Hell At My Command; Long, Hard Road; O.F.F.O - Outlaw Forever, Forever Outlaw

Skills:
Superb: (2) Craftsmanship, Fists
Great: (2) Driving, Intimidation
Good: (2) Conviction, Endurance
Fair: (3) Discipline, Athletics, Lore
Average: (5) Might, Guns, Lore, Resources, Weapons

Powers:
(-1) Demonic Copilot
(-2) Inhuman Recovery
(+1) The Catch: Swords of the Cross
(-6) Modular Abilities (4 Refresh worth)

Stunts:
(Craftsmanship) Bike Mechanic: +2 on Craftsmanship whenever dealing with a motorcycle or other bike, +1 on other personal vehicles (boats, cars, trucks, small aircraft).

Power Level: Submerged
Total Refresh: 1

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Background: Son of rural farmers, raised in southern Illinois on a soybean farm. The farm eventually went under and was bought by an agricultural corporation. The family lost everything and ended up living poor in Chicago. Though he was intelligent, he did poorly in school due to discipline and anger issues. He eventually dropped out of school and went to work as a mechanic. It wasn't long before his talent fixing motorcycles go him involved with the Outlaws MC "one-percenter" outlaw motorcycle gang, where his instinct with mechanical things, impressive strength and durability, and disregard for rules served him well.

"I Can Do Bad By Myself"

Rising Conflict: Descended into an orgy of violence, sex, and drugs, becoming so vicious he was called Mad Wrench (for his trademark of beating offenders with a 2 ft. wrench and his ability to fix his constantly breaking down bike) and placed into the SS, the Outlaw MC's squad of killers and enforcers. It also served to handle any "wierd stuff" the gang would run into, masking it behind the other violence regularly committed by them. During a conflict with RCVs, his natural ferocity and rage were noticed by the captain of the SS, Lil'Satan. He was taken as Lil'Satan's protege and eventually inducted into the Red Skulls, a secret society supposedly dedicated to destroying supernatural threats, but truly serving as Lil'Satan's personal loyalists. As part of his induction in the Red Skulls, he was granted the token of membership - a tarnished silver coin.

"Mad Wrench is Mad With A Wrench"

First Story: Too independent to be submerged under the Fallen Guziel, he was still heavily influenced, like being permanently affected by supernatural PCP. Over the course of several years, he led a band of the SS in cleaning out a nest of RCV (connected to the ones mentioned previously) who had infiltrated the Chicago Outfit (mafia). He truly came into his own, the knowledge of Guziel and the power of the Fallen allowing him to demolish the RCV infestation.

"Knowledge Of Hell At My Command"

Guest Star: Preacher-Man 10 years passed, and Wrench became the 2nd in command of the SS, he and Lil'Satan ruling their own personal feifdom within the Outlaws. Lil'Satan implemented his plan, attempting to take over the mainstream Outlaws, starting with the assassination of their leadership, but Preacher-Man (a fellow Outlaw, but deeply faithful) interfered, the power of his Faith staggering the Fallen. Fully himself for the first time in many years, Wrench fled, finding himself in the poor, rundown neighborhood of his childhood, at his elderly parents' door. His parents were terrified of him, and his rage flared, ending in their deaths. Stricken, broken, he raged against his own downfall and the Fallen in his mind, who for the briefest of moments, expressed sorrow. Holy Man arrived with a few members of the SS; Wrench begged forgiveness, vowing to earn redemption. Rather than cast aside the coin, he seize\ds upon the brief moment of remorse, determined to redeem not only himself, but Guziel as well.

"Long, Hard Road"

Guest Star Redux: Smiley Wrench and Preach systematically set about destroying the Red Skull members of the Outlaw MC, aided by certain in-the-know members. Their pursuit of Lil'Satan took them to St. Louis, where the last of the Red Skulls were slain with the help of a former SS biker and RCV Infected, Smiley. Lil'Satan's coin was encased in concrete and sank beneath the Mississippi. Rather than return to the main club, Wrench, Preach, and Smiley received permission to open a new chapter, which Wrench dedicated to hunting down the supernatural (and sometimes mundane) predators. He hopes to do enough good to wash the blood from his hands, but he's still an Outlaw at heart, loyal to the only family he has left.

"O.F.F.O - Outlaw Forever, Forever Outlaw"

But back on the topic of "is there Evil and Good" in the Dresdenverse, I think there is.  Dresden doesn't always recognise it when the forces of Good are moving but both absolutes exist in the books.  Then you have creatures like Mab, whose motivations are so obscure that she appears completely amoral.

It'll be a harrowing journey from there to redemption, but what's a PC without angst and long background arcs?