I love your ATLA KNB crossover! I was curious about your line of thinking b/c while I totally see how Akashi would bend lightning, I personally think Aomine and Akashi should switch, especially because of how although Akashi is cold and calculating for lightning, his emperor eye can control the opposing players' movements which imo make him more inclined to bloodbending, and Murasakibara seems more earthbender type to me (non-metal bending) bc he's all about being unmoveable and strong (tbc...)
I see what you’re saying here, and I totally agree! Honestly I really just liked the picture of Aomine as a really powerful waterbender... and I feel like he wouldn’t ever really use his bloodbending unless he really really had to. And when I think of Akashi, I think of prestigious and fancy, which in turn makes me think of firebenders. I see what you’re saying with the emperor eye thing though!!
And as for Atsushi, yes, he could be a great earthbender because he doesn’t wanna move haha. In my extended headcanon though, I see him as the only bender in his family. Because of this, they never really bothered to get him a teacher so he had to find his own. And he found Himuro, who I think would be a very level-headed firebender, pretty uncommon tbh. Himuro was able to teach Atsushi a unique way of waterbender, more similar to that of a firebender than a waterbender. I made Mura a waterbender mostly for this, because I wanted them to be opposites, but I think him being an earthbender is also a really good idea!