You can change events of any games, story campaigns and see the outcome and how it changes the world. You can start with a question "What if". What point of the story of would you like to change? Basically make a entrance start, and I will do the rest

Just says anime and crossover with it anything be a game such as Undertale or Warcraft whatever.

Example: Naruto or Fairy Tail x WarCraft or WarCraft x StarCraft....