I’m strong, I’m strong, I’m strong....!
Ren as he is is inherently a pacifist- he dislikes hurting people, and would much rather solve things with clearly communicated words than anything else (be it manipulation, threats, etc) if possible. Despite this, were he ever to become more combat oriented one would probably find that there are quite a few instances where he’d get quite carried away, especially on missions where he’s specifically ordered to protect something in a life-or-death scenario.
He just gets high on the idea of being able to prove himself. In a way, you could even accuse him of flashing back to when he originally died as a human and taking pleasure in knowing he’d be able to cut enemies down now. He’s been helpless in his previous life, weaker than all his friends and then some; and his resolution to become stronger now has probably gotten him romanticising the concept a little- despite the academy’s teachings, and despite his own temperament as well. Once Ren believes he’s doing the right thing in the name of people he cares about, morals and restraint often leave the picture completely after the first death. It’s unknown whether this would change if anyone ever noticed and tried to snap some sense into him.
It’s a slippery slope one he starts falling, and it’s in these moments that you realize just where exactly Urushi’s excitable nature comes from.