One possible plot is that Teddy, while exploring some old family artifacts, stumbles upon a charm that allows him to enter a realm where his father exists. His father might share stories about his time at Hogwarts and how he fell in love with Teddy's mother. They could also have an adventure together, fighting off some dark forces that are threatening the wizarding world's past.
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, 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, Teddy might be shocked by the Dursleys' coldness at first. He could show them some magic in a very subtle way, just to see their reactions.
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, 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.
Perhaps the Marauders are summoned by some dark force in Teddy's time. Teddy, having heard of their adventures, helps them figure out what's going on. They teach Teddy some of their old - fashioned spells and tricks, while Teddy shows them new ways of magic. Together, they face the dark force and emerge victorious, with the Marauders having to find their way back to their own time.
In the fanfiction, the Howler Teddy Lupin gets could be a case of mistaken identity. Some powerful magic could have misdirected the Howler meant for someone else to him. Teddy then has to figure out who the real recipient is while also dealing with the public humiliation of the Howler's scolding. He might start an investigation at Hogwarts, teaming up with his friends to solve the mystery and clear his name.
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, perhaps in the fanfiction, Harry adopts Teddy Lupin right after the Battle of Hogwarts. Teddy is just a baby then. Harry, who has lost so many people, sees Teddy as a new beginning. He might face challenges from the wizarding community as some may question his ability to raise Teddy. But Harry, with the help of his friends like Hermione and Ron, overcomes these difficulties and Teddy grows up to be a strong and kind wizard.
Well, it could be about Teddy having a dream where he meets his parents. In the dream, Remus and Tonks are as he's always imagined them. They tell him how proud they are of him, even though they didn't get to see him grow up. This simple encounter could be a very moving and emotional one, with Teddy waking up with a newfound sense of purpose and connection to his parents.