In a Danny Phantom Phantom Planet fanfiction, the ghosts can be very interesting to focus on. For example, Ember McClain. She has a unique power and her own backstory. You could write a story about her trying to regain her power or form an alliance with Danny. And then there's Skulker, the hunter. A fanfiction could explore his motives and how he might change his view of Danny after the events of Phantom Planet.
Sam and Tucker are really interesting characters to focus on. Sam's gothic personality and her strong beliefs can lead to some great storylines. Tucker's tech - savvy nature can be used in many ways, like developing new gadgets or helping Danny figure out some tech - related mysteries. And Jazz, Danny's sister, with her psychology knowledge could play a crucial role in understanding Danny's situation better in a fanfiction.
Danny himself is always a great focus. His dual identity as a normal teen and a ghost - fighting hero gives a lot of room for exploration in family fanfiction. His parents are also very interesting, especially their reactions to Danny's powers and how they could grow and change in a family - centered story.
A new character could be a foreign hero who comes to Amity Park to learn from Danny. They might have different powers and a different approach to ghost - fighting. Another possibility is a scientist who is intrigued by Danny's powers and wants to study him, not in a malicious way, but out of pure scientific curiosity.
A great fanfiction idea could be a time - travel story within the Danny Phantom Phantom Planet universe. Danny somehow gets sent back in time to before he became a half - ghost. He has to figure out how to get back to his own time while also dealing with the knowledge he has of the future. This could lead to some really interesting interactions with his past self, his family, and friends. And he might accidentally change things in the past that could have a huge impact on the future of the Phantom Planet.
Obviously, Danny and Dan themselves are very popular. Danny as the main hero and Dan as his dark and complex counterpart are central to many stories. Jazz, Danny's sister, is also popular as she can provide a different perspective and often gets involved in Danny's ghost - fighting adventures in fanfiction.
One idea could be exploring Danny's new role as a hero on a global scale. Maybe he has to deal with new threats that are attracted to his increased fame. Another could be delving into his relationships with his friends and family after the big events in Phantom Planet. For example, how does his relationship with Sam and Tucker change now that he's a more public hero?
Kim Possible herself. She's a strong, independent character. In a fanfiction with Danny Phantom, she could be the one to teach Danny a thing or two about being a hero without superpowers (at least in the traditional sense). Her determination and resourcefulness would be a great contrast to Danny's more impulsive use of his powers at times. Plus, seeing her react to the supernatural elements of Danny's world would be fascinating.
Obviously Danny himself is a must - include. But also Sam and Tucker are great characters to have. They've been with Danny through everything and can add some great human - side to the fanfiction. Valerie could also be included. She has her own complex relationship with Danny and the whole ghost - fighting thing. And of course, there are the ghosts like Vlad. His rivalry with Danny can create a lot of interesting storylines.
Danny himself is an obvious choice. His journey through different realities can bring out so many different aspects of his character. He can face new challenges that test his limits as a half - ghost. Sam and Tucker are also great characters to focus on. They can provide support to Danny in different ways in each reality. Jazz could also be interesting as she might have different relationships with Danny in different realities. And then there are the ghosts like Vlad who could have different motives and actions in alternate realities.
Obviously, the main character would be Danny Phantom himself, but in two different forms or versions. One would be the original Danny Phantom from the canon source, and the other would be a version created by the fanfiction. There might also be his friends like Sam and Tucker who could play important roles in helping the two Dannys understand each other and deal with any issues that arise from their meeting.
Sam is also quite popular. Her goth - like personality and her strong - willed nature make her an interesting character. In fanfiction, she can be portrayed in different ways, like being even more involved in Danny's ghost - fighting activities.