The main character is James Sirius Potter. As for the Marauders, James Potter would be important as he's James Sirius Potter's father. Sirius Black would bring his wild and rebellious nature into the story. Remus Lupin with his kind heart and werewolf secret could add depth. And even Peter Pettigrew, despite his later actions, would be part of the group dynamic in the fanfiction. There might also be other characters from Hogwarts during the Marauders' time or James Sirius Potter's time who interact with them.
In this fanfiction, perhaps James Sirius Potter could learn some of the classic pranks the Marauders were famous for. He might get into all sorts of adventures, following in their footsteps and causing a bit of chaos at Hogwarts just like they did.
Obviously, Albus Potter and the Marauders - James Potter, Sirius Black, Remus Lupin and Peter Pettigrew. There might also be some other characters like Albus's friends or professors who could be involved in the story.
There could also be some minor characters from the Marauders' era that might become more prominent. For example, Lily Evans, Harry's mother. Her relationship with James and how she might interact with Harry in this strange time - traveling or spirit - meeting scenario could be really interesting. And then there are the Hogwarts professors from both eras that could be involved, like Professor McGonagall, who could either be a guiding force or be a bit skeptical of Harry's new interactions.
Obviously, Ginny Weasley is one of the main characters. She's a strong - willed and brave witch. The Marauders, which include James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew, are also likely to be main characters. They are known for their mischief - making and loyalty to each other. Dumbledore might also make an appearance as he was around during the Marauders' time and would surely have some role to play if Ginny is interacting with that era.
Well, aside from Teddy and the Marauders, there could be other characters as well. Maybe some of Teddy's friends or classmates from his own time who are somehow involved in his journey to meet the Marauders. For example, if Teddy discovers a time - traveling spell in the library with the help of a studious friend. But the core characters would still be Teddy Lupin and the Marauders. Teddy is the link between the present and the past in this story, and the Marauders are the ones with all the stories and experiences from their time at Hogwarts.
One possibility could be that Snape meets James Sirius Potter in a Hogwarts flashback scenario. Maybe James Sirius Potter discovers some old memories or secrets related to Snape through a magical object. This could lead to a whole new understanding of Snape's character for him.
One possible scenario could be that McGonagall meets James Sirius Potter in a Hogwarts corridor. She might be reminded of his father, James Potter. She could give him some sage advice about living up to the Potter name and the importance of using his talents for good, just as his father did in his own way.
Obviously, the marauders themselves - James Potter, Sirius Black, Remus Lupin and Peter Pettigrew. They would be central to the story as they are the ones the fanfiction is named after.
His father, Harry Potter, might also send a Howler. Harry knows the importance of discipline and responsibility, and if James was shirking his duties or not following the rules at Hogwarts, Harry would not hesitate to use a Howler to communicate his disappointment and expectations.
In some fanfictions, other characters like Dumbledore might also play important roles. He could be the one who arranges the encounter between Harry and the Marauders, either knowingly or unknowingly. And Hermione and Ron might also be involved in some cases, perhaps helping Harry understand the implications of meeting his father and his friends from the past.