Obviously, Albus Severus himself is the main character. His friends from his own time might also be involved in some way, like Scorpius Malfoy. And of course, the younger versions of well - known characters like Harry Potter, Hermione Granger, and Ron Weasley are likely to appear.
We can't forget about the villains. Voldemort or his followers might make an appearance. Albus Severus could find himself in a situation where he has to face them without the full power he has in his own time. Or he might even try to prevent some of their evil deeds from happening in the first place, which would put him in direct conflict with them.
Another plotline could be Albus Severus trying to correct a mistake made by one of his ancestors. This might involve him interfering with a family feud or an old magical spell gone wrong. As he travels through time, he has to be careful not to disrupt the fabric of time too much, which adds an element of danger and suspense to the story.
Luna Lovegood's daughter could be a potential girlfriend. Given Luna's unique and open - minded nature, her daughter might inherit those traits. She could be someone who is interested in the same mysterious and off - beaten - path aspects of the wizarding world as Albus, and they could bond over that. Their relationship might also be a connection between two different generations of Hogwarts students.
Obviously, Yusei himself. And his friends from his original time period might also show up in flashbacks or if he somehow brings them back in time with him. For example, Jack could be there.
Obviously, Twilight Sparkle herself. And her friends like Rainbow Dash, Pinkie Pie, Fluttershy, Rarity, and Applejack might also be involved. Maybe they follow Twilight back in time or she has to work with past versions of them.
Ron is also a common character. He could provide the comic relief as well as be part of the adventure with Harry. Dumbledore might also show up as he is the wise mentor figure. Harry might seek his advice on how to handle the changes he wants to make in the past without disrupting the future too much.
Maybe there are local characters in each place she visits. For instance, in France, she meets a charming baker who teaches her how to make the perfect croissant. In Thailand, she befriends a tuk - tuk driver who shows her around the hidden alleys of Bangkok. There could also be other travelers she meets along the way, sharing stories and tips about their own travels.
Some of Annabeth's other demigod friends from Camp Half - Blood might make an appearance. For instance, Grover could come to the school undercover to check on Annabeth and make sure she's okay in the mortal world. He could also help her out if there are any nature - related problems at the school.
There could be a wise old hermit who lives in a secluded forest that Ash meets during his solo travels. This hermit might have a deep knowledge of Pokémon lore and give Ash some valuable advice.
One possible antagonist could be a dark wizard from the past who somehow catches wind of Albus Severus' time - traveling and decides to use his knowledge of the future for his own evil purposes. Maybe a forgotten Death Eater who was thought to be dead but actually survived in hiding and now sees this as an opportunity to rise again.
Obviously, Josuke himself would be the main character. His friends like Okuyasu could also be involved. Maybe Okuyasu somehow follows Josuke back in time or Josuke has to find a way to bring him back if he gets left behind in the past.