Hell, you want a story? Actually make the leap to make Finn an unaware Force-sensitive, and give him a minor version of The Exile's power, deeply bonding with those around him entirely by instinct. Eventually after breaking the conditioning, he deserts, rescuing Poe, and is deemed a traitor. As he tries to survive going forward, he's forced to kill a lot of First Order troopers, and causing so many of their deaths will feel like he's stabbed himself in the heart.