Ken may initially drift between Minato, Ryoji, and Lancer as he sees fit. Eventually though he'll break off from them and start heading out on his own, since he doesn't want to be around them once the mass killing starts.

His main issue is that he's going to be reluctant to kill anyone. It's likely that in a full-on fight he may hesitate. That said, even if he's grown in Animus he's still pretty young, if that's something that would stop your character.