Karai

Before the "Enemy of My Enemy" episode, Karai was more calm and even offered the turtles a temporary alliance. But when they broke the pact, Karai became more cruel, more ruthless, and wanted to kill Splinter and the turtles at any cost, just like Shredder. Karai was also quite inhumane; for example, she wanted to kill the innocent April in revenge for her mother's death. She also treated those below her in rank, such as Xever and Bradford, with no respect.

Everything changed when she found out that Splinter was her real father, Karai became kinder, but she still remained vengeful and wanted to take revenge on Shredder herself, which ultimately led to her mutation.

In Season 4, Karai remained vengeful and did everything in her power to destroy Shredder. She was also quite overconfident and rarely enlisted the help of her friends, hoping to destroy Shredder's empire alone, which often led to her defeat.