So looking at Zuko 1st. He had a traumatic childhood to say the least. He translated this into aggression, hyper focus on regaining his honor and proving himself to Ozai, and is an all together angry young man with a touch of megalomania.
Mai also had a traumatic childhood but in a wildly different manner. Her issues were verbal with a hyper controlling environment where she was literally not allowed to be a kid. All her actions had to be for her father's advancement. This left Mai bitter and Incredibly closed off
Also, Mai is female and most likely grew up just waiting for a son to be born to take her birthright. The fire nation seems like it would maintain a patriarchy. So she represses emotions, only having a little bit of fun during a fight or destroying something.
So while Zuko is angry and loud with his emotions, Mai is his polar opposite. Keeping all emotion on lockdown, not allowing herself to want for much so as not to take up space.
BUT PUT THESE TWO TOGETHER AND....
BUT PUT THESE TWO TOGETHER AND....
Zuko finds a partner that puts him in his place when his issues come out as jealousy. And he challenges Mai to open up and be more compassionate. They have their moments of toxicity, but inevitably they talk it through and grow.
They both go from these damaged kids to ooey gooey teenagers who just wanna climb a mountain and have a picnic together.
They respect each other. Zuko didn't confide in Mai about his choice to leave the fire nation to help Aang, and when she could tell he had a major decision she didn't push him to talk, she comforted him. And when Mai might need help, Zuko knows she can handle anything.
While Zuko betrays his father, Mai betrays everything to save Zuko. Knowing full well Azula would more than likely kill her for it. If Ty Lee hadn't stepped in we all know she would have been murdered. Ultimately these two are stronger together, and I'm stupid happy for them.