Definitely Naruto and his friends like Shikamaru. Shikamaru, being the smart strategist, often plays a role in helping Naruto make important decisions as an adult in fanfiction. Also, characters like Kakashi might still be around in some fanfictions, acting as a mentor or an advisor to Naruto in his adult leadership role. And of course, the new generation of shinobi such as Boruto may also be included, showing the relationship between Naruto as a father and his son.
Charlotte's family members could also be main characters. Her parents, for instance, who have influenced her upbringing and continue to be part of her life as she grows. They might be shown guiding her through different life decisions or having their own story arcs that intersect with Charlotte's.
It often depends on the original source material. If it's based on a kids' show, then the main characters would be the grown - up versions of those from the show.
Well, Ralphie is surely one of the main characters since it's about him all grown up. His family members from his childhood might also make appearances, like his parents or his brother. They could play important roles in showing how Ralphie's past and present are connected during Christmas.
Ralphie himself would be a central character, of course. His parents might also make an appearance, either in his memories or in person if they are still around. His wife and children could be important characters as well, as they are part of his new family life during Christmas.
Maybe a young apprentice of Hinata. A girl who is inspired by Hinata's grace and strength. This character could bring a fresh dynamic as she looks up to Hinata and also gets to know Naruto. Additionally, there could be a mysterious figure from a far - off land who comes to the Hidden Leaf and has an unexpected connection to Naruto and Hinata's story.
Tommy is often a popular choice. Since he was kind of the leader in the Rugrats days, it's interesting to see how he grows up and takes on more responsibilities as an adult. His relationships with the other characters can also be explored in different ways.
Another idea is that all the characters are now parents themselves. They have to balance their work at Monsters Inc with raising their own little monsters. It could show how they use their experiences as scared kids or scarers to be better parents.
I'm not sure specifically as there could be many novels with this title. But generally, it might be about the journey of characters as they transition from childhood to adulthood, dealing with new responsibilities, relationships, and self - discovery.