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.
A really cool plot twist might be that Tom Riddle travels to a future where Voldemort never existed. Without his future self's influence, the wizarding world is a very different place, full of peace and harmony. But his presence in this future starts to stir up old, dark desires in some people, and he has to decide whether to continue his old ways or embrace this new, positive world.
Perhaps a plot twist is that in the future, magic has evolved in ways he couldn't have imagined. Tom Riddle, who was used to being a powerful wizard in his time, finds himself outclassed by new forms of magic and has to learn from the future wizards to survive. This would turn his expected journey of superiority into one of humility and growth.
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.
One possible plot twist could be that Tom Riddle's dark tendencies start to resurface despite Hermione's positive influence. Maybe he begins to secretly manipulate those around him at Hogwarts while still maintaining a facade of being a reformed child. This could lead to a rift between Hermione and some of her friends who suspect Tom but don't understand why Hermione is so trusting.
One common plot twist is that the pregnancy might be part of a dark plan by Tom Riddle. Maybe he intended it to gain some sort of power or to manipulate Hermione in a more complex way. Another could be that Hermione discovers something unusual about the baby that links it to a greater mystery in the wizarding world.
One interesting plot twist could be that Hermione's teachings accidentally lead Tom Riddle to an even darker path. Maybe she teaches him advanced magic that he then uses in unexpected and malevolent ways. For example, he could use time - turning magic she showed him to manipulate historical events to his advantage.
One possible plot twist could be that Tom Riddle discovers Harry has a hidden power that he didn't expect. Maybe Harry has the ability to resist Riddle's mind - control spells in a unique way. This could lead to a battle of wills between them where Harry tries to outwit Riddle while being held captive.
A possible plot twist could be that Tom Riddle actually becomes a mentor - like figure to Severus Snape in a fanfiction. Riddle, seeing Snape's talent for the Dark Arts, decides to guide him in a different way than the Death Eaters would. This would completely change the way we view their potential relationship.
Well, perhaps the plot could involve Hermione actually getting through to Tom Riddle in some way. Since she's so intelligent and empathetic, she might start to make him question his dark ways while being kidnapped. This could lead to a really interesting internal struggle within Tom. Also, there could be a twist where the kidnapping is part of a much larger plan that involves other dark wizards or witches, and Hermione has to figure out how to not only escape but also stop this bigger conspiracy. Or it could be that Hermione discovers a secret about Tom Riddle's past during her captivity that she can use to her advantage.
One plot idea could be that Hermione travels back in time and tries to prevent Tom Riddle Jr from becoming Voldemort. She might use her knowledge and magic skills to change his path. Another could be a scenario where they meet in an alternate universe where the rules of good and evil are more blurred, and they form an unlikely alliance to face a greater threat. Maybe Hermione gets trapped in a magically created world by Tom Riddle Jr, and she has to outwit him to escape and in the process, she discovers some hidden secrets about his past that could have changed his future.
Well, perhaps in the fanfiction, Hermione as a Veela has the ability to enter Tom Riddle's dreams. In his dreams, she shows him the consequences of his future actions as Voldemort. This makes Tom start to have doubts about his planned path of evil, and he has an internal struggle between his dark desires and the newfound influence of Hermione's Veela presence.
One idea could be a time - travel fanfic where Harry goes back in time and tries to prevent Tom Riddle from becoming Voldemort. He could try to befriend the young Tom and show him a different path. Another could be a fanfic where Harry and Tom are somehow trapped in an alternate dimension together and have to work together to escape, all while Harry tries to understand what made Tom turn so evil. A third idea is a fanfic where Tom Riddle actually has a change of heart early on due to some magical accident that makes him experience a different kind of love and kindness, and Harry has to deal with this new Tom in Hogwarts.