To explain a little what this is before things get started, because I feel like this is a confusing setup.
The following story was the winning run (written by me but ported to AO3 cause I feel like others might appreciate it) for r/WhoWouldWin's Ninth Character Scramble. The Character Scramble is a fanfiction writing tournament wherein all competitors submit so many characters (of a specific power level), the characters are thrown into a pot, scrambled, and then everyone is given a completely randomized team around which their story will center. Each round then has your team fight another person's team, and people vote on whoever wrote the best story. This Scramble's theme was Fate/Grand Order, which basically means important historical setpieces are where each round takes place, and each team has a Master who summons and controls the rest of their team.
The actual story will get into all this stuff, that should be all that's needed to explain what in the hell is happening here.