Ideas for Crossover Stories

It’s no secret, I love crossover stories. It expands the human imagination of story telling. Whether it’s within said universe or different worlds colliding. The kinds of crossover stories I like to read and/or write about are the ones that could logically make sense while others would do so either for fan service or just for pure fan fiction. Through this, I like to post and offer any scenarios about logical but sound and fun ideas that people would like to hear or try to write about. The criteria can be as follows:

1. Takes place within its universe or it can be across the different universes.

2. Characters have to have certain similarities between them (ideals, powers etc.)

3. Doesn’t have to be romantically involved, but I consider more of friendships and connections made between them.

4. Can usually have a common foe that unites them (heroes or villains)

All suggestions and/or comments are welcome.