Warning: This post contains spoilers for Dexter: New Blood.
In Dexter: New Blood, Dexter decides that Harrison has his own Dark Passenger and will become a serial killer as well - but the ending suggests that Dexter might have been wrong. At the end of Dexter season 8, Dexter fakes his own death and leaves Harrison with Hannah McKay who takes him to Argentina. In Dexter: New Blood, Harrison tracks his father down after almost a decade and forces him to face his past.
In the final episodes of Dexter: New Blood, Dexter reveals his killings to Harrison and begins to teach him the code. Dexter has come to the conclusion that as Harrison was “born in blood” by seeing his mother die in the same way as Dexter that he too has a Dark Passenger and will be driven to take his actions further and start to kill. Harrison is enthusiastic about the idea of killing to protect the lives of others; however, when he realizes that Dexter kills for his own pleasure and self-preservation, he insists Dexter turn himself in, but Dexter instead asks Harrison to shoot and kill him.
While Harrison is shown to be angry and violent throughout Dexter: New Blood, it is only Dexter’s narration that assures the audience that he truly has a Dark Passenger. Harrison is never seen to have the visions that Dexter talks to and, though claims to have Dexter attacked people in self-defense, appears to have never actually killed before. Before the finale, Harrison never actually kills in Dexter: New Blood: he hurts Ethan badly, breaks a wrestling opponent’s arm, and he watches Dexter kill Kurt. While Dexter is eager to attribute Harrison’s lashing out to a Dark Passenger, Harrison’s final speech suggests that it is more traditional teenage lashing out amplified by the anger of his father having abandoned him and not returned for a decade. It is Dexter that has made Harrison volatile through his decisions, and it is Dexter who finally makes Harrison a killer by asking him to kill him.
It is of course possible that Dexter will be proved correct retroactively. It is conceivable that based on the lore of Dexter Harrison might develop a Dark Passenger owing to the events he witnessed in Iron Lake and killing his own father. While this idea would help to drive a narrative for Dexter: New Blood season 2, it might be a betrayal of the Dexter: New Blood season 1 finale as it leans so much into Harrison’s anger being caused by Dexter and Dexter’s sacrifice being geared towards giving Harrison his freedom.
A major theme in the second half of the original run of Dexter is the question of where a Dark Passenger comes from and whether it can be disposed of. Dexter season 5 affirms that it comes from trauma and can be removed by confronting that trauma through the narrative of Lumen (Julia Stiles). However, later seasons suggest that Dexter’s Dark Passenger might be too deeply embedded, and Dexter could be too far gone to recover, while Deb questions whether the Dark Passenger is even a real thing or just Dexter’s excuse for killing. The Dexter: New Blood season finale doesn’t address this directly, but if Harrison were to return in the future, the possibility of redemption is still on the cards and the finale ultimately gave closure to the fact that Dexter didn’t pass his Dark Passenger on to Harrison, or at least not in the way that he feared he might have.