You could also write a fanfiction about the 'little king' traveling to different realms. He might encounter unique cultures, strange creatures, and have to adapt to new magic systems, which would make for an exciting adventure.
One idea could be exploring the backstories of minor characters in more depth. For example, you could write about the early life of a demigod who was only briefly mentioned in the original series. Another idea is to create alternate endings to the main story arcs, like what if the heroes had made different choices during a crucial battle? You could also focus on the relationships between the characters in a different light, perhaps showing a friendship that was hinted at but not fully developed.
A fanfiction could also focus on the backstories of the less - explored characters in Dragon Ball Heroes. For instance, you could write about the origin of a particular alien race that is only briefly mentioned in the game. Explore their culture, their reasons for getting involved in the battles, and how they interact with the main characters. This would add more depth to the overall Dragon Ball Heroes universe.
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 fanfiction could focus on how the ponies form an unlikely alliance with some of the Storm King's minions. They realize that they also don't like the Storm King's tyrannical ways and decide to work together to overthrow him. This would involve a lot of character development for both the ponies and the minions.
One idea could be exploring an alternate universe where Naruto's parents didn't die. This would change his whole upbringing and how he views the world. He might not be as driven to become Hokage in the same way, and his relationships with characters like Iruka and Sasuke could be very different.
A great fanfiction idea is to have the heroes of Olympus time - travel. They could go back to the time of the ancient Greek heroes and interact with them. Maybe Percy meets Theseus and they have to compete in some sort of challenge. Or the story could focus on a character like Nico di Angelo and his journey to discover more about his powers in a place that is off - limits to most demigods, like the Underworld's deepest secrets. There could also be a fanfic where the demigods have to deal with a curse that affects their powers in strange ways.
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.
Perhaps there's a situation where the heroes of tomorrow are suddenly stripped of their powers. They then have to rely on their wits, training, and teamwork more than ever. They find out that an old enemy from the original Avengers' past has developed a technology that can nullify superpowers. Now they have to figure out how to get their powers back and stop this enemy before it's too late.
A great plot idea could be a time - travel plot. What if one of the heroes accidentally travels back in time to before they got their powers? They could try to prevent a certain event that led to the creation of a super - villain. Or, perhaps a hero gets sent into a parallel universe where the roles are reversed and the villains are the heroes. This would force them to reevaluate their own beliefs and actions.
One idea could be a fanfiction where the characters play a magical version of truth or dare at a party. Each dare could involve using their demigod powers in a fun and unexpected way.