I did post this trope some time ago but one more time won't hurt, I'm always interested in seeing some more examples since I really like it whenever I see it. So let's get on with this.
1-2 - Undine (Claymore) - the first time we see her is when she acts cocky towards weaker claymores gathered to combat extremely powerfull monsters, claiming they would only drag the stronger warrriors down. She also claims to be the strongest of all the claymores despite being number 11 (11th strongest out of 47) and thinks her weaker comrades would only force her to babysit them.
Turns out that in the past she was a feeble warrior who found solitude in her close friend and survived thanks to them. But it was her friend who died in battle instead of her, and Undine was too weak to protect her, leading to a lot of survivor's guilt. Undine took her friend's sword (which is why she's the only one with two swords) and swore to avenge her by becomming the strongest warrior. Her guilt is why she doesn't want the weaker claymores to fight directly, she doesn't want to loose anyone close to her again, especially those she feels responsible to protect.
Also yes, both images are the same person, she's not naturally buff, only uses her powers to make herself buff when around others, but turns skinny and frail when alone without altering her body.
3-4 - Hellion (Darkest Dungeon) - she's the most outwardly agressive of all the heroes in the game, as the narrator describes her: "Barbaric rage and unrelenting savagery make for a powerful ally".
When she was young her people set an ambush, but she was too afraid to fight, resulting in the death of all the warriors beside her. The reason she's so agressive is to show both to her dead comrades and to herself that she's not a coward (now i haven't played Darkest Dungeon 2 which i know adds more context so sorry if i miss something. I also know that a lot of the story, including characters' backstories is purposefully vague and open for interpretation, so there's also room for misinterpreation).
5-6 - Zuko (Avatar The Last Airbender) - a banished prince of the Fire Nation. Ever since we meet him he has a very short temper and severe anger issues. Even his own crew sees him as an asshole.
We learn that he was banished for showing care for the lives of young soldiers sent to their death, disrespecting his father in the process and refusing to fight him. He was labeled a coward and banished only allowed to return if he captures the Avatar.