Edited to add the following:

Although he retains a similarly calm, stoic demeanor to his previous incarnation, he's extremely untested in comparison; while he has no trouble remaining impassive and cool under when faced with a dissection in bio lab or the pressures of finals week, he has nothing like his previous experience as a warrior and it remains to be seen whether he can face true violence as easily as he did before. The closest Hajime has ever come to a fight is pushing back when another kid in middle school tried to push him into a locker, and the closest he's come to command is taking the initiative over his lab partners in classes. It's still in his nature to face everything as calmly as possible and apply reason to what happens rather than let his emotions get the best of him, but he lacks the experience in the kind of situations that would truly push him to the limits of his patience and ability to keep a clear head.

If there's anything else you feel I ought to address that I didn't, I'd be glad to add to it further!