With Talion's past as a Ranger, this makes perfect sense for a combat tutorial. The intro to the game could be either Talion learning everything he knows from Aragorn or vice versa. It doesn't need much more of an explanation than that and the idea that one of these guys learned everything they knew about combat from the other would lend Talion some tough guy credibility from the offset. Outside of this, flashbacks to his Ranger days could feature encounters with the king of men in hiding, maybe even conversational foreshadowing between the two about their respective fates. Talion is clearly intended as a much darker version of the main trilogy's heroic ranger and comparisons between the two would serve to highlight how different a character within Tolkien's works Talion is intended to be.