One idea could be to have heroes from different universes team up to fight a common, powerful enemy. For example, Superman from DC and Thor from Marvel joining forces.
A possible idea for a Fire Emblem Heroes crossover fanfic is to cross it with the Final Fantasy series. The characters from Fire Emblem Heroes could enter the world of Final Fantasy and encounter iconic summons like Ifrit or Shiva. They could also participate in battles against the likes of Sephiroth. Another option is a crossover with the Pokémon world. The Fire Emblem Heroes might befriend Pokémon and use them in battles, or they could be on a quest to stop an evil organization that's misusing Pokémon power.
A crossover with a superhero universe, say the Marvel Universe. Travis Touchdown from No More Heroes could find himself in New York City and get involved with the Avengers. Maybe he initially misunderstands their motives and gets into a fight with them, but then realizes they're on the same side against a greater threat.
A great concept for Harry Potter heroes crossover fanfiction would be to cross them with the characters from the Star Wars universe. Picture Hermione using her intelligence to outwit Darth Vader. Or Harry learning some Jedi mind tricks. Also, a crossover with the characters from the Percy Jackson series. The demigods and the wizards could have an interesting interaction. Maybe they could combine their powers to defeat a common foe that threatens both the magical and the mythological worlds.
One idea could be a crossover with the Naruto universe. The Saiyans could learn about chakra and how to use it, while the ninjas are amazed by the power of ki. Another could be a time - traveling plot where the Dragon Ball Heroes characters end up in the past of their own world and have to prevent a major catastrophe that changes the course of their history. Maybe a crossover with One Piece where they search for the One Piece together and face off against the powerful pirates and the Marines.
A cool plot for dc super heroes crossover fanfiction could involve Wonder Woman and Aquaman. Maybe there's a threat that endangers both Themyscira and Atlantis. They must combine their unique skills, like Wonder Woman's combat abilities and Aquaman's control over the sea, to save their respective homes. Also, a Martian Manhunter and Cyborg crossover could be interesting. The Martian Manhunter's shape - shifting and telepathy, along with Cyborg's technological prowess, could be used to stop a cyber - psychic threat.
One idea could be a new prophecy that involves the demigods having to travel to an unknown realm to retrieve a powerful artifact before the Titans use it to destroy the world. Another could be a fanfic where the demigods form an alliance with some previously thought - of - as - enemies, like certain monsters who also don't want total chaos. Or perhaps a story where a demigod discovers a hidden power within themselves that has the potential to change the balance of power between the gods and the Titans.
A uzumaki crossover fanfic could involve crossing over with 'Bleach'. Picture an Uzumaki character in the Soul Society, their strong chakra being mistaken for reiatsu. They could bring new fighting styles and techniques to the Bleach universe.
One idea could be a crossover with 'Naruto'. Gon could meet Naruto and they could have a friendly competition in terms of strength and speed. Another idea is a crossover with 'One Piece', where the Hunters from 'HxH' join the Straw Hat Pirates on an adventure. Maybe they could be searching for a rare treasure that has both the allure of the Grand Line and the mystery of the 'HxH' world.
One idea could be a Dalek crossover with the Doctor Who companions. Imagine the Daleks facing off against a group of companions who have to use their unique skills and knowledge to outwit the Daleks. Another could be a crossover with a science - fiction adventure like Star Trek. The Daleks' aggressive nature would contrast greatly with the more diplomatic Starfleet.
One idea could be a crossover with 'Friends'. Jerry could visit Central Perk and have a stand - up comedy session there. His unique sense of humor might either amuse or confuse the 'Friends' gang.