Pokemon
Set in the Yokoh region, whose league is known to be viciously competitive. Any of the 16 gyms can be challenged in any order (scarlet/violet stole this from my brain actually,) and the gym leaders will adjust their teams to match the skill level of their challengers. Due to their unique gym structure, there are many special rules for Yokoh's league, but trainers native to the region also have a reputation for being very strong because of their difficult league. World