Spookberry's Very Cool Pokemon OCs

Basically the important part is that its been split down the middle in some way, either a river or a mountain range or a completely arbitrary border both sides have agreed to.

Depending on which game you pick you either start on side A or side B. Each side has four gyms and after you beat them you have to cross the divide to get to the other side. Gameplay wise this means each gym leader has two different teams, the one they use for side A players and the one for side B players. The team used against othersiders is significantly harder than the one they use for their own.

This is because both halves of the region HATE each other.

Obvi Your rival comes from the other side, i kinda like the idea of there being two different rivals. You meet both but which one you meet first depends again on which version you play. Personally i like the idea that one was from side B but has lived on side A now long enough that people view them as being one of them and side B's think theyre a traitor. I think if this was a real game theyd make the player the outsider. But!! i like the idea more so that your second "friendly" rival is the one whos new to the region and doesnt really get the animosity.

The legendaries have some sort of forbidden love story that was lost to time and has been misremembered as the origin of each sides animosity towards the other.