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.
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.
Medic from TF2 and Mercy from Overwatch. They're both healers, but they have very different approaches. Medic is a bit more... unorthodox with his healing methods, like using his Medi - Gun. Mercy, on the other hand, is more angelic and serene. It would be fascinating to see how they interact, perhaps they could learn from each other's techniques and develop new ways to heal the combined team during a tough battle.
Well, it could be about an Infamous character getting thrown into the Overwatch universe. Maybe they have to team up with the Overwatch heroes to fight a common enemy like a new, powerful omnic threat. The Infamous character might bring their unique powers, like electricity - based abilities, and have to learn to work with the diverse group of Overwatch characters, each with their own personalities and skills.
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 fanfic could be set in a post - apocalyptic world where the TF2 characters are the last line of defense against some new, powerful threat. The Heavy and Medic have to work together to develop new strategies and weapons. Their relationship is put to the test as they face difficult decisions and moral dilemmas.
Mercy from Overwatch and the Medic from TF2 would be likely allies. They both have a strong focus on healing. Mercy's ability to fly and revive teammates could be well - complemented by the Medic's Ubercharge ability. Another pair could be Tracer and Scout. They are both fast - moving characters. They could use their speed to scout out areas, steal intel or make quick strikes against the enemy.
I think Mercy from Overwatch and Medic from TF2 could be great allies. They both have a strong focus on healing and could share medical knowledge and techniques from their respective universes. Mercy's ability to fly and revive teammates could be combined with Medic's ÜberCharge in interesting ways during battles.