>>281516892
The answer to that is, the first four fighters were all part of the same stable, therefore ineligible to fight each other.
Everyone else he fought was a newcomer to the colosseum, apart from Vivian who was a low-level jobber that was never expected to fight the high-ranking fighters, therefore Zulu didn't account for the possibility that she'd fight the MC.
It's also explained that these "undefeated fighters" are usually made to fight no-hope slaves/isekai'd dudes with no skills, to make them look stronger than they are. Alice for example had never been in a real fight, and Mary only fought isekai "spawns" with garbage skills.
It's a corrupt colosseum where the top fighters are built up in the same way as in boxing, by making them fight bums, and occasionally fixing the fights and tipping off the nobles about it.
