When the MC becomes evil in a sci-fi/fantasy, it's pretty easy to have them turn around and start blasting away at everything they felt wronged them; going on giant killing sprees while ranting about how the world treated them like shit, so they're giving the world exactly what it deserves. The problem is, when the setting is in our world, the MC can't exactly do that. Case in point: in my General Mysteries set in modern times, the MC (Kevin McKinley) discovers the last thing about himself that he ever wanted: he enjoys seeing those he feels are criminals at his mercy, he enjoys the power he has on them. Think Frank Castle from The Punisher, only Kevin isn't going around murdering everyone left, right, and center. This is more of a deconstruction of The Punisher if anything else. The idea is that Kevin McKinley discovers this side of himself and slowly but surely begins to descend deeper and deeper into that side until he realizes he's gone too far and tries to redeem himself. Now unlike Frank Castle, Kevin doesn't have access to every single military-grade weaponry to unleash hell. At best, his weapons are a knife and a pistol. That's it. Not exactly I'm-The-Punisher-All-Shall-Fear-Me style. He's a college-aged student living with his aunt, uncle, and middle-school aged cousin. So my question is, how do I realistically go about having him go from a generally kind-hearted individual to becoming a vigilante who takes pleasure in causing his enemies emotional distress (he doesn't kill them) without blatantly ripping off of The Punisher? Thoughts?
For maximum drama, a trigger event - he reacts violently, realizes it's satisfying, and continues. For more realism, a slippery slide into violence. He does something small, likes how it feels, does something a little bigger, and then a little bigger after that. Eventually, he's a full-on vigilante.
I like the slippery-slope approach. He excuses his actions until something happens, like say he shoots a guy because he thinks the guy is a criminal and it's at that point he realizes he might have gone too far. Maybe something big happens that then makes him want to redeem himself, but he feels he's gone too far to go back. Would it be cliched to have his friends be horrified and going, "You've gone too far, man! What the hell!?" And have Kevin push them away? I hope this isn't a spoiler but...a part of me kind of plans to model him after Darth Vader, only his big redemption act involves fire.
Seems to me it's more likely his friends won't know anything about it, and as he descends into vigilanteism he'll start avoiding them and pushing them away. I don't know anything about The Punisher, but this sounds a little like Dan Wells' I Am Not a Serial Killer. I'm not mentioning this to discourage you, but to suggest something that might give you some ideas. I doubt Mr. Wells would mind.
He could have a moment when he's doing something terrible that seems justified, but then he finds out/realizes that his victim isn't really a bad guy after all. In Mad Max: Beyond Thunderdome, Max is dueling to the death with the big baddy ("Blaster") in the Thunderdome. Blaster is always masked, and nearly kills Max, but when Max rips off the armored mask, he sees that Blaster is (I'm struggling for a non-offensive word) mentally challenged? Far from being the incarnation of evil, he's basically just a little kid trapped in a huge body, doing the bidding of Master, the little person who rides his shoulders.
Robert de niro as a vietnam veteran with PTSD driving a taxi whilst planning to assainate a senator to impress cybil shephers character, but instead eventually recues jodie fosters character from her drug dealing pimp. His amament is basically four handguns - its definitely worth a look The other thing about acquiring hardware is that if he's killing criminals he could take their weaponry - it doesnt take much skill to use a pump action shotgun, or for that matter an automatic weapon.
I didn't think of that. If Kevin starts having no qualms about murdering his criminals, why would he not take their weapons as well?