I thought it might be worth discussing the game itself. The instant I saw the illustration* I thought of the Aztec ball game, ullamaliztli, and knew that there would be deaths involved. There's a pretty good explanation here. Politically the Aztec game seems to be the closest match we have, though play-wise the game Sister Ultimately-Justice makes her own seems to have somewhat more in common with volleyball, with the distinct player zones, though the scoring across a goal-line is more handball-ish (I was completely confused as to who had won the final point as I initially read it as out-of-play in the soccer or tennis sense).

*It's disappointing from the access side of things that there's no alt-text to explain the image for people who can't see it.