A really popular 'kids next door crossover fanfic' is the one that crosses over with 'Powerpuff Girls'. The Powerpuff Girls and the KND join forces. The fanfic plays with the different abilities of each group. Blossom, Bubbles, and Buttercup's superpowers blend well with the gadgets and teamwork of the KND.
The clash of different universes. For example, if it's a 'kids next door' crossover with 'Teen Titans', the different powers and personalities make it exciting. Robin's leadership in the Teen Titans against the more chaotic but organized KND is a great dynamic.
Sure. There are probably some really interesting characters. Maybe there's a curious and adventurous kid who always gets into fun situations. There could also be a shy but kind-hearted one who has a great friendship story to tell.
A great plot might involve the kids forming a secret club in high school that's like a successor to their Kids Next Door operations. They face challenges from a rival high - school group who also have their own 'undercover' activities. The story could focus on the battles between the two groups, both academically and in their secret missions. For example, competing for control over the school's abandoned attic which they both want for their own purposes.
Another option is to have Hinata and Numbuh Three as the main characters. Hinata's shyness and her growth in Naruto could be paralleled with Numbuh Three's own journey of self - discovery in the KND. They could support each other and show different aspects of courage in the face of challenges.
One idea could be a crossover where the Naruto characters visit the world of the Kids Next Door. Maybe Naruto and his friends join the KND in one of their missions against the adults. Another idea is to have the KND use some of the ninja techniques from Naruto, like Naruto teaching them how to do the shadow clone jutsu.
Another interesting fanfic could be about a KND agent going undercover in an adult - like world. For example, an agent has to infiltrate a high - society event to stop a plot that involves using grown - ups to take over the world of kids. It would be full of comical situations as the agent tries to blend in while still being a kid at heart.
One idea could be a time - travel fanfic where the Kids Next Door go back in time to the origin of their organization. They could meet the first generation of operatives and learn the true roots of their fight against adults. Another idea is a crossover fanfic, like with another popular kids' show. For example, having the Kids Next Door interact with the characters from 'Avatar: The Last Airbender'. They could team up to fight a common enemy, perhaps an adult - led group that wants to control both the world of the Kids Next Door and the four nations in 'Avatar'.
Numbuh One is a popular choice. As the leader, he has a lot of responsibilities and his leadership skills can be explored further. For instance, you could write about his decision - making process during a difficult mission.
Another one is 'Vegeta in the Harry Potter World'. Here, Vegeta has to adapt to the magical environment. His initial confusion and then his determination to master the magic (in his own way) is really fun to read. The way he interacts with the Hogwarts students and teachers is full of comical and exciting moments.
One great 'Lucina crossover fanfic' is 'Lucina in the World of Fire Emblem Heroes'. It has an interesting plot where Lucina gets transported to the Heroes' realm and teams up with various characters from different Fire Emblem games. The story is full of action and character development.