Lance pokes fun of Shiro being a merman (not an actual merman unfortunately), and pidge and hunk, defending their father’s honour, dares lance to take some of Shiro’s classes (he teaches people how to become merppl n all that w allura).
Lance takes the dare and finds out this guy from one of his classes, whom he has a one-sided rivalry with, goes for mermaid lessons as well and *insert oh no he’s hot moment here*
anyway there’s lots of pining and swimming and mermaids and keith being obsessed with the mythical merpeople n lance finding it endearing as hell
[edit:] I’m not planning to write this however I will be building upon this au If you wanna write this or whatever could you link it to me? I wanna see it :D