I am rambling as opposed to writing a structured Meta, so bare with me.
But I have noticed the theme of “Choice”, and how it relates to Arima and Kaneki.
In Jack, Arima presents himself as someone that lacks choices. He explains that he simply goes where he is told to go, and does what he is told to do. When his cover is compromised, he explains to Fura that he will be sent away. He admits that he enjoyed being able to attend school and be around people his own age……but his superiors won’t allow him to stay. Fura refuses to accept this, and argues that Arima’s secret is safe and he should stay. Arima actually takes this to heart, and seems to have convinced his superiors to let him finish the mission.
But once Lantern has been eliminated, he can no longer stay. He tells Fura he will be leaving soon, and sent to his next mission. He doesn’t know where he’s going, and matter-of-factly states that he may die next time. For such a young man, he is already resigned to being powerless when it comes to his own life.
Arima is a person with no choice, or at least he presents himself as such.
In contrast, when it comes to his protege, he has repeatedly defied his superiors to offer him choices.
Arima makes a point of having his new protege choose his own name. He encourages him to take this first step himself, choosing the Kanji that would stand for his new identity.
Now we see Arima again pushing Kaneki to choose. He could have killed Kaneki many times over during their battle, but instead he spends much of their battle either observing him or lecturing him about his lack of conviction.
He’s placing things firmly back into Kaneki’s hands, forcing him to confront reality and decide what he really wants. He states what HIS choice will be, that he will kill Kaneki’s friends if he simply gives up and dies.
What he isn’t stating is whether he even wants to kill Kaneki or not. He has kept his thoughts to himself, and allowed his protege to remain confused about him all these years. But at the very least, it seems like there is some part of Arima that sees importance in Kaneki being able to choose for himself in the way Arima himself never was able to.