What if… There was a justice league au for the legend of korra. I mean think about it,
Asami could be batman; she’s rich, doesn’t have bending/powers, is extremely smart, can build anything, always puts her life on the line for the sake of others, runs her own company.
Korra could be superman; they are both the most powerful beings, extremely hard to beat, born with their powers, multiple types of powers.
Mako could be the flash; the Barry Allen kind of flash, a vigilante, always looking for justice, when he isn’t the flash he’s a cop, reds his color, his hair has a blown around look to it that fits so well.
Bolin could be green lantern; the Hal Jordan kind of green lantern, I imagine he would make silly things with his ring and it amuses me, he becomes great friends with superman, he would risk everything to keep the world safe, greens his color too so that helps.
Opal could be Wonder Woman; many writers have depicted Wonder woman in different personalities and tone; between that of a warrior, a highly compassionate and calm ambassador, and sometimes also as a naive and innocent person. What has remained constant is her ability to feel compassion and give love without discrimination.
Kuvira could be Martian Manhunter/J'onn J'onzz; J'onzz is very strong, he is often used as a substitute for superman in other comic books, Kuvira rivals Korra in strength as J'onzz rivals superman.
Iroh could be Aquaman; while yes it is the wrong element, I was running out of people to use and I like iroh. Plus it’s an au so whatever. Aquaman is from Atlantis royalty and Iroh is from fire nation royalty. Iroh is introduced as the captain of a navy fleet Aquaman is a water superhero, the connections are there.