A lot of Demons have Angel counterparts, who are destined to be rivals... usually in a stronger sense than Sports Rivals like these two are though. Unlike Demons, Angels spend their time encouraging focus, aggressively seeking to eliminate all distractions one might have, regardless of how actually important what one is doing is. As such, the Sports Angel focuses nearly exclusively on Sports.
The Sports Angel seems to think highly of Sports Mastery rather than the enjoyment of the game. They spend most of their time in intense practice, focusing on single aspects of the games at a time, seeking mastery in the art of Sport. Of course, they encourage just about everyone they meet to join them in seeking Sports Mastery. They generally aren't too much of threat though, especially given how much they keep to themselves while practicing...
Obviously bitter rivals with the Sports Demon, they're generally pretty evenly matched, and frequently challenge eachother to exhibition matches that are quite popular among dedicated fans in the Demon and Angel population, and essentially unheard of to basically everyone else.
Beyond that... basically save boat as the Sports Demon really, not quite sure if they have a name and don't really have any strong opinions on what gender they probably are, although I guess probably agender. They don't play on the same court as gender, they're too busy playing on the tennis court.