In this kind of fanfiction, perhaps Teddy Lupin discovers a magical way to time - travel and meets his father. It could show Teddy learning about his father's character and values through their interactions. Maybe his father teaches him some unique magic that was passed down in the family.
It could be a dark wizard who is trying to prevent Teddy from meeting his father. This wizard might be afraid that Teddy will gain some powerful knowledge or magic from his father that could be used against him.
Well, Teddy could learn a great deal about his family's history from the members of the Order. Maybe he'd discover some hidden secrets or untold stories.
Well, it could be about Teddy Lupin traveling back in time and meeting his father's friends, the Marauders. Maybe he gets to experience their pranks first - hand and learns some new magical tricks from them.
Well, one possibility is that Teddy, being the son of Remus Lupin, would likely be filled with a sense of justice. He might immediately be on guard around Umbridge. Since Umbridge was known for her cruel and unjust ways at Hogwarts. Teddy could use his Metamorphmagus abilities to play tricks on her, like changing his appearance to something that scares her when she's being particularly mean.
It could be a rogue Death Eater who escaped justice and is now seeking revenge on the Order and anyone related to them. So, Teddy, being Lupin's son, would be a target.
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.
At first, it might be a bit awkward. Teddy has only heard stories about Remus, and Remus is seeing this young man who is his son in a way he never expected. But as they start to talk, they would find common ground in their love for magic and their experiences at Hogwarts.