One idea could be the Overwatch heroes being transported to the RWBY world. They could team up with Team RWBY to fight a new common enemy, like a powerful Grimm that is immune to normal attacks but vulnerable to Overwatch tech. Another plot could involve a character exchange, where a RWBY character like Ruby goes to the Overwatch world and learns about their technology and fighting styles, and then brings back new knowledge to her own world.
Well, a cool concept for an Overwatch RWBY crossover fanfic would be to focus on the technology aspect. Overwatch has a lot of advanced tech, and RWBY has its own unique Dust - based technology. The fanfic could explore how the two types of technology interact. For instance, Mercy's healing staff could be affected by Dust in the RWBY world, or Torbjörn could use RWBY - style materials to upgrade his turrets. And of course, the character interactions would be great. Winston and Zwei could be an interesting pair to write about.
A more complex plot could involve a mysterious force that is causing glitches in both worlds. Some characters from Overwatch and TF2 have to work together to figure out the source of this force. For example, Tracer from Overwatch and Scout from TF2 could use their speed to scout out the affected areas while their respective teams of engineers, like Torbjörn and Engineer from TF2, try to fix the glitches in the technology.
One idea could be an Overwatch crossover with the Star Wars universe. Imagine Tracer using her time - traveling abilities in the middle of a lightsaber duel. Another could be a crossover with the Harry Potter world, like Pharah flying on her rocket launcher over Hogwarts. And a crossover with the Marvel universe, where Reinhardt teams up with Thor to fight some powerful villains.
One plot could be that a powerful artifact has been discovered that has the potential to change the balance of power in both the Overwatch and Team Fortress 2 universes. Characters from both sides start to hunt for it. There could be double - crosses and alliances formed along the way. The Soldier: 76 from Overwatch might initially see the Red Team from Team Fortress 2 as enemies, but as they realize they have a common goal, they start to work together. Meanwhile, the Sniper from Team Fortress 2 could be in a sniping competition with Widowmaker from Overwatch as they also search for the artifact. This would create a mix of competition and cooperation in the story.
One idea could be that the RWBY characters are transported into the Overwatch universe and have to team up with the Overwatch heroes to fight a new common enemy, like a powerful omnic - Grimm hybrid. Another could be a friendly competition between the two groups in a series of combat trials to see who is more skilled.
A crossover with a cyberpunk - themed story could be really cool. Genji's cybernetic enhancements would fit right in. He could be on a mission in a dystopian city, facing off against powerful corporations and their enforcers. Along the way, he might meet new allies who are also fighting for justice in this harsh environment.
Another concept could be a story where a character from Halo, say Master Chief, gets transported to the Overwatch universe. He has to adapt to the different rules and powers there while trying to find a way back home. Along the way, he could form unexpected alliances with Overwatch heroes and learn about their world, and they could learn from his military discipline and combat experience.
Another interesting concept could be a crossover in which the technology from TF2 is integrated into the Overwatch universe, or vice versa. For example, the Medic's healing technology being used to enhance the Overwatch medics' abilities. This could lead to some really cool character interactions and story developments as they learn to work with new equipment and each other.
A great concept could be a crossover tournament. The two teams, TF2 and Overwatch, compete in a series of challenges. These challenges could include things like a sniper - only round where Widowmaker from Overwatch and Sniper from TF2 go head - to - head. Or a melee combat round with Reinhardt and the Demoman. It would be a chance to explore the different abilities and personalities of the characters in a competitive setting.
Maybe the villains from BNHA team up with some of the evil forces in the Overwatch world. Then the combined good guys, including both BNHA heroes and Overwatch agents, have to figure out how to defeat this new, dangerous alliance. It could lead to some really cool battles and character interactions, like All Might facing off against Doomfist.