Another possibility is a powerful magical creature that has been awakened or created in the future. This creature, with its own motives and powers, could oppose Tom Riddle as he tries to navigate this new future world. For example, a magically - enhanced golem that was created to protect the future wizarding society from threats like Tom Riddle's arrival.
Maybe it's a group of future Ministry of Magic officials who have become corrupted by power. They view Tom Riddle as an anomaly from the past and fear that his knowledge of old magic could disrupt their control over the wizarding world, so they become the main antagonists in his journey.
Tom Riddle himself could be the main antagonist. Even in his school days, he was showing signs of his future as Voldemort. His dark thoughts and actions towards other students or his exploration of dark magic could put him in direct opposition to Harry.
One interesting plot twist could be that when Tom Riddle travels to the future, he discovers that his name has become a symbol of great evil, and he has to face the consequences of the actions his future self took. This forces him to re - evaluate his own path and potentially change for the better.
You could also create a fanfiction where a new character, an orphan just like Tom, arrives at the orphanage. This new character could either be a positive influence on Tom, trying to show him kindness and friendship, or they could be in competition with him for the limited resources or attention in the orphanage. This would add a new dynamic to the story of Tom Riddle in the orphanage.
The main characters are obviously Tom Riddle and Ginny Lemon. Tom Riddle is often portrayed as a complex and dark character. He is highly intelligent but also extremely power - hungry. Ginny Lemon, on the other hand, is usually depicted as a brave and somewhat headstrong character. She may be written as a character who is not easily intimidated by Tom's dark presence.
Tom's character could become more vengeful. Meeting his father, who may have abandoned him, could make him more determined to prove his worth and power. He might see his father as a symbol of all those who have wronged him, and this could lead to a more rapid descent into darkness.
Hermione Granger is often a popular character. She can use her intelligence to figure out the implications of time travel and help Harry or deal with Tom Riddle in some way. For instance, she might research spells to counteract any dark magic that Riddle tries to use during their time - traveling encounters.
In addition to them, there could be other characters from the original 'Harry Potter' series who play important roles. For instance, Dumbledore might still be a guiding figure in Harry's life. He could be suspicious of this new friendship between Harry and Tom and try to keep an eye on them. Hermione and Ron could also be part of the story, either supporting or being skeptical of Harry's new friendship with Tom.
They can interact as students. For example, if they time - travel to when Tom Riddle was at Hogwarts, they could be in the same classes or clubs. Maybe they join the Duelling Club where Tom Riddle was known to participate. Another way is through chance encounters in the hallways or the library. They could strike up conversations about magic or Hogwarts history.
Tom Riddle might be very suspicious at first. He is a very intelligent and cautious person. He would likely view time travelers as a threat to his plans or as a strange new phenomenon that he wants to control. So, he could start by trying to figure out their motives and how they managed to travel through time.
The 'lemon' in a Tom Riddle and Hermione fanfiction could be a metaphor for the unexpected. For instance, Hermione might find a lemon - like a magical object - that has some connection to Tom Riddle's past. This object could hold secrets that bring them closer in an unforeseen way. It could start as a simple mystery but turn into a more complex relationship as they explore the significance of this lemon - related item.