One interesting crossover could be the combination of TF2's unique character classes with Overwatch's diverse heroes. For example, the Scout from TF2 could have a race against Tracer from Overwatch. Another could be the Medic from TF2 teaming up with Mercy from Overwatch to heal a group of both TF2 and Overwatch characters in a chaotic battle scenario. Also, the Engineer from TF2 might build structures in an Overwatch - like map to help both teams' forces.
A really cool crossover would be the Spy from TF2 infiltrating an Overwatch base. He could steal some of their advanced technology and cause chaos among the Overwatch heroes. Meanwhile, Widowmaker from Overwatch might be tasked with taking out key TF2 characters. But things get interesting when characters like the Pyro from TF2 show up and just start causing mayhem, disrupting Widowmaker's plans.
One interesting TF2 Overwatch fanfiction could be about a crossover battle where the characters from both universes accidentally meet in a strange dimension and have to fight together against a new, unknown threat. For example, the Engineer from TF2 and Torbjorn from Overwatch might team up to build some amazing defenses.
First, you need to understand the characters from both TF2 and Overwatch well. Know their personalities, abilities, and backstories. Then, come up with an interesting plot that can involve both sets of characters in a meaningful way. For example, a threat that only they can defeat together. Also, don't forget about the unique humor in TF2 and the more serious tone in some parts of Overwatch. Try to blend them well.
One idea could be an Overwatch crossover with the Star Wars universe. Imagine Tracer using her time - jumping ability in the middle of a lightsaber duel on Tatooine. Another could be a crossover with the Harry Potter world, where Winston, being the intelligent gorilla, might be intrigued by the magic at Hogwarts and try to study it. And a crossover with the Lord of the Rings, with Reinhardt as a valiant knight facing off against Orcs in Middle - earth.
Another theme is the exploration of different game mechanics. Writers often play with the idea of how the TF2's class - based system and Overwatch's hero - based system could coexist or clash in a fanfic story. It can lead to really interesting scenarios and battles. And also, the theme of teamwork or lack thereof between the two groups is often explored. Since both games have elements of teamwork, seeing how the characters from different games work together or against each other is quite fascinating in fanfics.
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.
One interesting crossover could be the characters' abilities. For example, in some fanfictions, a character from Overwatch like Tracer might use her time - jumping ability in the Star Wars universe. Maybe she helps the Rebel Alliance by going back in time to prevent a crucial event from happening in favor of the Empire.
Another possibility is that there's a rift in time or space that brings the two universes together. The TF2 and Overwatch characters find themselves in a strange new world that's a mix of both of their own. They have to figure out how to get back to their respective universes while also dealing with local threats. Some characters might be tempted by the different cultures and powers they encounter, which could cause internal conflicts within the combined group.
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 great TF2 and Overwatch fanfic is 'The Mercs and the Heroes' which combines the unique characters from both universes in an action - packed adventure. It has interesting crossovers and character interactions.