While watching The Super Mario Bros Super Show, I came across an episode called like the title, about Mario and Luigi origins as plumbers. During the talking with the recruits by Sergeant Kooperman, you can see two plumbers, next to Mario and Luigi, who greatly resemble Wario and Waluigi!!
So, adapted to the present, you can imagine the same scene: the Mario brothers and the Wario brothers entering the same academy and their rivalry still burning.
Hope you like it
Reference image: www.mariowiki.com/images/0/0a/…