Ok, first it's been more than 2yrs since I somehow read that manga and i'm not sure if it was scanlations or just raw, so POSSIBLE SPOILERS

So i think there is two females cops/agents who are pretty strong and a guy got involve involuntarily with them (he is weak at the beginning). Then, at some point, one of the girls dies (got killed) and it impacted the guy who decided that he wanted to be strong and not be unreliable. So he goes into some military style boot camp and become strong and came back to be part of the team....and hmmm well that's all i can recall so far.

😀 

i think that the manga you are searching for is ZeroIn 😀

Splendid Core Splendor...that was it! Thanks 😁

well actually another question..do you know when do the weak guy gets some real training...as far as i can remember it was hardcore training, but so far in the scanlations...he does get some training in a ring, but he doesn't become what I remember so far.