It’s been pointed out for a while that Kylo Ren in The Force Awakens has a fixation on Finn that turns increasingly to rage. These moments include:
*Noticing Finn at Tuanul village and intimidating him by unfreezing the blaster beam from Poe’s rifle
*Realizing immediately that Finn was the Stormtrooper who had escaped with Poe
*Flying into a rage at the mention of Finn escaping Jakku with BB-8
*Purposefully inflicting pain and maximum injury on Finn during the lightsaber battle in the woods
What I haven’t seen mentioned is that right after Ren killed his father Han Solo, he recognized Finn and was enraged enough to go after him despite being badly wounded. I didn’t put this in my recent edit because the context would not be clear enough, and I think a text explanation is necessary to show what was going on.