Potentially, a seer or a fortune - teller in the past could interact with Caroline. They might have some knowledge about her time - traveling situation or be able to give her clues on how to get back. Another character could be a young inventor or a magician's apprentice. They would be interested in Caroline's modern ideas and try to incorporate them into their work in the past. And her own ancestors, if she travels far enough back, would be very important characters. She might have to protect them from a threat in the past to ensure her own existence in the present.
One type of character would be the local townspeople in the time period she visits. They can show her the ropes of that era, introduce her to their culture and way of life. Then there are the antagonists. Maybe there's a power - hungry person in the past who wants to use Caroline's knowledge of the future for their own gain. Also, a love interest from the past. This person could be a nobleman or a simple farmer, but they would be drawn to Caroline's different nature and they would have a relationship that develops as she tries to navigate the past.
Jiraiya could also be a character that Karin interacts with. Jiraiya is always on the lookout for knowledge and new techniques. Karin, coming from the future, could have some valuable information for him. They might bond over their shared love for the Uzumaki clan's secrets or Karin could learn some new jutsu from Jiraiya in the past. And of course, Tsunade. Tsunade is a powerful figure in the Naruto world. Karin could seek her help or advice in the past, and Tsunade might be interested in Karin's future knowledge especially regarding medical ninjutsu which both of them are associated with.
Sasuke would be a likely character to interact with Naruto as a Time Lord. Their complex relationship in the original Naruto series would add an extra layer of drama in a time - traveling scenario. Another could be Kakashi. His wisdom and experience would make for interesting conversations with Naruto, especially when Naruto has the power of a Time Lord. And of course, Jiraiya. Given his close relationship with Naruto and his own adventurous spirit, he'd be very involved in Naruto's time - traveling adventures.
Definitely Naruto and the Punisher first. Naruto would be intrigued by the Punisher's methods and would try to understand his motives. It's also possible that Sakura could interact with the Punisher. She's a strong - willed character, and she might try to either stop the Punisher if she thinks his actions are too extreme or help him if she sees the good in his goals. And Jiraiya might also be a character who could cross paths with the Punisher. Jiraiya's worldliness and his own sense of right and wrong could lead to some deep discussions between them.
Naruto, of course. Since they are in the same team in the original story, it's very likely that Sakura will interact with Naruto. She might try to change his fate or help him in a different way. Sasuke is also a main character she'll interact with. Maybe she'll try to prevent Sasuke from going down his dark path. And Kakashi, as their teacher, will also be involved in their interactions.
They are likely to interact with Naruto's past self. It would be an interesting dynamic as Naruto tries to explain things to his younger self without messing up the timeline too much. And Himawari would be there, perhaps teaching her young father some of her own jutsu.
Natsu would be a very likely character. Since he and Lucy are close friends in the original story, if Lucy travels back in time, Natsu might be one of the first people she seeks out. They could have adventures together in the past, with Natsu being his usual impulsive self and Lucy having to keep him in check with her knowledge of the future.
Definitely Hagrid. Hagrid has always been around Hogwarts and has a connection to the students. Sirius could interact with Hagrid if he goes back in time. Maybe Hagrid could help Sirius in some way, like providing shelter or information. And Bellatrix Lestrange could also be in the picture. Since she is part of the Black family, Sirius might have to deal with her in the past, either to try to change her or to stop her from doing something evil.
Shinji is a very likely character. His complex relationship with his father and his role as the main pilot make him a prime candidate for time travel scenarios. He could go back in time to try and fix things or understand his father better.
Tony Stark is a likely focus. His intelligence and experience with technology, especially time - travel technology in the movies, make him a central figure. He could be the one to figure out the mechanics of time travel and lead the Avengers in their time - traveling adventures.
Obviously Caroline herself is the main character. Her mother is likely to be in it as well, as mothers often play an important role in a girl's first period experience, like giving advice and support.