Sam Manson would be an excellent addition. Her strong - willed and goth - like nature can add an interesting dynamic. From the Kamen Rider side, if we consider Kamen Rider W, Shotaro Hidari could be included. His detective skills combined with Danny's ghost - hunting abilities would make for some great mystery - solving scenes. And let's not forget Jazz Fenton, Danny's sister. She could provide some emotional support and also get involved in the action in her own way.
Another great character to include is Vlad Masters from Danny Phantom. His half - ghost nature and his complex relationship with Danny can create a lot of drama. In terms of Kamen Rider, Kamen Rider Kabuto with his cocky and confident attitude could be a fun addition. When paired with Danny, they could have some great battles and power - struggle moments, especially if they have different ideas on how to handle the threats that arise in the fanfiction.
Cisco Ramon from the Flash's universe would be a great addition. His ability to create new gadgets and his sense of humor would fit well in a crossover. For Danny Phantom's side, Frostbite could be included. His knowledge of the Ghost Zone and his ice - based powers could be crucial in a story where they are facing a powerful enemy. Also, including the Reverse Flash as a villain would create a lot of tension and action in the fanfiction.
Obviously Danny and Rouge are the main ones. But Tucker could be a great addition. He could provide some tech - support or comic relief. And for Rouge's side, maybe Shadow could be included. Shadow could add an element of mystery and power to the story.
Sam is a great character to include. She often provides a different perspective to Danny and Tucker's adventures, and her environmentalist views can add an interesting dynamic, especially when dealing with ghosts that are related to nature or pollution.
One interesting story could be about Danny Phantom getting the powers of a Kamen Rider and using them to fight supernatural threats in both his world and the Kamen Rider world. He might team up with a Kamen Rider to take on a powerful ghost - demon hybrid villain.
Some fanfictions could focus on the characters' personalities. For instance, a story could be about a Kamen Rider befriending Danny Phantom. The Kamen Rider might be initially skeptical of Danny's ghost powers but then come to respect and rely on him as they face challenges together. Danny, in turn, could learn a lot from the Kamen Rider's sense of justice and determination.
Tucker would be a great addition. He could provide some comic relief with his tech - savvy ways. He might also be able to upgrade their ghost - fighting gear. Sam is another good one. She could offer her unique perspective on things, especially when it comes to environmental and ethical issues. And of course, Vlad could be included as the antagonist. His devious plans and power - hungry nature always make for an interesting conflict.
Obviously, Danny Phantom himself is a must - he's the main character. Then, the Control Freaks are essential as they are the focus of this particular fanfiction. Tucker and Sam are also great to include as Danny's friends. They can provide support, different perspectives, and sometimes comedic relief. Jazz could also be added, maybe she gets caught up in the Control Freaks' schemes in a way that forces Danny to act to protect her.
Characters from Kamen Rider Decade are also frequently included. Decade has the ability to travel between different Kamen Rider worlds, so it makes sense for him to be in a 555 crossover. His presence can introduce new story elements and bring different Kamen Rider series together in a single fanfiction.
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.
A powerful and corrupted former Kamen Rider could be a great antagonist. Maybe someone who was once a hero but was consumed by power and now wants to take over the world using their Rider abilities for evil. They would know all the tricks of the trade and be a formidable foe for Phantom.