Definitely Ben Tennyson. He's the center of the Ben 10 universe, so it's no surprise he's often in body switch fanfics. When his body is switched, it's not just about the physical change but also about how he'll use his alien forms in a different body. Gwen is also commonly involved. She has her own set of skills and a distinct personality, which can be a great contrast when she's in someone else's body. Then there are the various alien characters from the Omnitrix. If they end up in Ben's body or vice versa, it can create all sorts of chaos and interesting plotlines.
Ben Tennyson is almost always the main character in 'ben 10 muscle growth fanfic' since it's based on the Ben 10 series. His transformation and the resulting muscle growth are central to the story. Sometimes, his alien forms might also be involved in a different way because of the muscle growth concept.
Ben Tennyson would definitely be one of the main characters as he is the central figure in the Ben 10 series. Gwen, his cousin, could also be involved as she is often by his side in the original series. Kevin Levin might also be part of it, especially if the story involves a more complex web of body swaps and relationships among the main characters.
Ben is obviously the main character as it's a 'ben 10' related fanfic. His various alien forms are also important characters in a sense. For example, Upgrade might be involved if the story has to do with his feet being able to attach to and control machinery in a unique way related to his feet. Gwen could also be a part of the story, perhaps helping Ben understand some strange phenomenon related to his alien feet forms.
In 'ben 10 body switch fanfic', the idea of character development is quite engaging. As they adapt to the body switch, they might learn more about themselves and others. They could discover hidden strengths or weaknesses in their new forms. Also, relationships between characters can change significantly. Friends might view each other differently, and enemies might gain new insights into their foes. This can create complex and dynamic storylines.
The Cullens are often involved too. Edward, for example, as Alice is part of the Cullen family. Their interactions can be explored in different ways in fanfic, perhaps showing a different side of their family dynamic.
Naruto is almost always the main character in 'Naruto Foodgasm Fanfic'. His love for food is well - known in the original series, so it makes sense. Sometimes his friends like Choji, who also loves food, are involved too.
Obviously, Tsuna is the main character. But often, his friends like Gokudera and Yamamoto are also involved. Since Tsuna's anger usually has something to do with his relationships with them, they play important roles in the fanfic. For example, they might be the ones who trigger his anger or the ones who have to deal with the consequences of his anger.
In addition to the main Naruto crew, characters like Jiraiya can be important in 'prodigious naruto fanfic'. He was Naruto's mentor, so in fanfics that explore Naruto's growth further, Jiraiya is likely to be there. Also, villains like Orochimaru or Pain can be central in some fanfics, especially those that deal with Naruto facing greater threats or trying to redeem the villains.
Another character that can be involved is Kakashi. He might be the one who discovers Naruto has been hypnotized and uses his wisdom and skills to try and reverse it. Also, characters like Sakura could play a role. She may be worried about Naruto and try to help in any way she can, like researching about the hypnosis or providing medical support if needed.
Obviously, Tenten is the central character as she is the one who is pregnant. In many fanfics, Rock Lee might be involved. Since they are comrades and friends from the same village, he could be there to offer his support or protection. Maybe he helps her with daily tasks when she starts to find it difficult due to her pregnancy.