Looking for a drama where the protagonist is the new guy/girl in the gang and either stirs things up because of hisher personality, the way heshe does things, or whatever, or heshe is mysterious, keeps secrets, etc.

Basically anything that makes you go: wth is heshe going to do this episode to mess up the dynamics of the original gang.

Really want to see something like the above but where the new guy is a total noob, fresh from the university/academy, and does things hisher way and has hisher own ideas, and is confident in those, and succeeds despite constantly being doubted and resented by the original crew.

(Someone please invent a gender neutral pronoun... ive seen some use "their", but that just confuses me)

Maybe Holyland? It's a great drama, but it has a somewhat different atmosphere from what you described. The main character is not so confident in himself, but he loves boxing and he wants to make a place for himself in the underground world through his own means.
Well, it's not exactly a gang technically, but the main MC in  You're All Surrounded fits that completely perfectly.  It's about the main MC, and a group, who became Detectives, he has a mysterious background, he has a specific purpose in mind, which involves secrets he is keeping about his past, and he kind of runs against the grain of the rest of the team.
I remember you
Who are you (2013)
Prosecutor Princess
Heroes - japanese drama

if you're into medical drama
- Doctor X
- God Hand Teru