I mean, so far all water benders in the animated team avatars have been girls, with the only exception being Kavik from the Yangchen novels and even he admitted he didn’t know much about healing, so if (in potential future seasons) they’re gonna defy the previous series tropes regarding team avatar this one feels like a must, specially given the water tribe’s traditions on gender roles and the fact that we’re seemingly going to see a lot of such subversions, such as twin avatars and the fact that an Earth avatar’s first mentor will be a millitarized air bender (should be fire but I take it since they're not exactly in any position to be picky in that regard).

Now a recurrent theme in the water tribe is it being particularly strict when it comes to societal and gender norms as well as loyalty to the kin and we've seen how toxic this could be in both series (women not beig allowed to fight, Yakone trying to "make a man" out of his sons, their collectivist mindset breaking Kavik's family) so it would be interesting to see how this mindset has affected them in a post apocalypstic world were they're seemingly no longer a nation. The fact that benders seemingly get conscripted, that water avatar seemingly caused the apocalypse and that water bending should be vital for water purification and recyclying as well as pacifying dark spirits and healing people from their poisons, would certainly make for an interesting exploration of a water tribe character in the main cast.

Say... I could see such a character as a particularly skilled water bender boy (close to Nisha and Pavi's age if perhaps a bit older) who specializes in healing whose expected to fulfill an existing role (which itself might be what drove him to train) despite his not wanting to but unlike the more rebellious Katara, Kalyaan and Korra (and for that matter Toph) or the more nostalgic Kavik and Sokka, he has begrudgingly accepted his role in society due to feeling the need to be useful to his kin. As he meets Pavi (who ought to beinterested in learning to heal), Nisha and Yae, the twins ask him to be their water bending teacher, though to remark his water tribe mindset and to differentiate him from Toph, he is far more hesitant to join them, at least innitially; perhaps joining a whole season later.

Now to adress the elephant in the room, I know this character isn’t part of the established cast, which for that matter seems to include a couple of characters of water tribe descent but none of them explicitly male so I don’t think such a character will be part of the main cast in the first season, which makes sense given that they’d be bound to focus on Yae looking after the girls and teaching them air bending. There’s even talk of no team avatar among the fandom, and though I feel this would be a terrible idea if they wanted to make a long term series, I do admit that for a 26 episode series might not be ideal for developing a 4+ character cast. Still I do believe that if the series gets more seasons, as was the case with Korra (which was originally gonna be 1 season long) and as I have no doubt the creators hope for, then the main cast could easily be expanded to include more characters.

• In fact, if there is a major timeskip to show the girls growing older and more mature they'd be bound to have teammates closer to their age to serve as peers rather than guardians like Yae, who for that matter would by then see the girls less as little sisters/daughters and more as teammates and eventually leaders.