One possible plotline could be that Professor Riddle, perhaps a relative of the infamous Voldemort (Tom Riddle), initially has a strained relationship with Harry. He might be suspicious of Harry due to his family connection to the Potters. However, as the story progresses, they could discover they have more in common than they thought, like a shared interest in some arcane magic. And they might end up working together to solve a mystery within Hogwarts that threatens the entire wizarding world.
Another plot could be that as Harry raises Tom, he discovers some hidden good in Tom that was overshadowed by his later actions as Voldemort. Harry might then use this discovery to try and rewrite the future, preventing all the destruction that Voldemort caused. He could encourage Tom's magical abilities in a positive way, like getting him involved in helping others with magic instead of using it for domination.
Perhaps in the fanfiction, Harry adopts Tom Riddle when he's still a young boy at the orphanage. Harry then uses his own experiences of growing up without parents to bond with Tom. He teaches Tom about magic in a different way than Dumbledore did, focusing on the positive aspects of magic for good. This could lead to Tom not becoming the evil Voldemort we know.
Well, a possible plotline might involve a spell gone wrong. Maybe Hermione is researching a powerful and ancient magic and accidentally gets connected to Tom Riddle's essence from the past. Or it could be a situation where she is transported to a different dimension where Tom Riddle is not fully evil yet and they have an encounter that leads to her pregnancy. However, all of these are very much against the grain of the original story and its themes.
Their first encounter might be full of tension. Harry, being aware of the name Riddle and its association with Voldemort, would be on guard. Professor Riddle, on the other hand, might be intrigued by Harry's fame. He could approach Harry with a certain air of mystery, perhaps asking him some probing questions about his past and his abilities. Harry would likely respond defensively, creating an immediate sense of unease between them.
One possible plotline could be that Harry, having seen the destruction Tom Riddle caused as Voldemort, decides to take young Tom under his wing to prevent him from going down that dark path. He could introduce Tom to the love and friendship he never had, like the friendships Harry formed at Hogwarts. This new environment and positive influence might change Tom's view of the world.
A plotline could involve them going on adventures outside of the wizarding world. They could travel to different magical realms, encountering strange creatures and magic systems. Along the way, they learn more about each other's strengths and weaknesses. Harry might learn from Tom how to be more strategic, and Tom could learn from Harry about the importance of loyalty and friendship. Their friendship could be tested in these new and dangerous situations, but ultimately it could grow stronger.
One possible plotline could be Harry initially resists the idea of being Tom Riddle's submissive mate but gradually finds himself drawn to Riddle's power and charisma in a complex way. Maybe they are forced to work together against a common enemy and during that time, their relationship evolves.
One possible plotline could be that Harry, being a wizard from the magical world of Harry Potter, somehow gets involved with the dark and supernatural world of Hellsing. His magical abilities might be a source of both intrigue and conflict. Maybe he uses his magic to help the Hellsing organization in their fight against vampires and other dark creatures, and during this process, he falls in love with a character from Hellsing and they get married.
Maybe Harry leaves the wizarding world and uses his magical skills in the muggle world as a mercenary. He could be hired for dangerous jobs that require a touch of magic but need to be kept secret from the muggles.
A possible plotline could be that Harry's basilisk - related Animagus form is a result of some ancient magic that was dormant in him. The Ministry of Magic might see this as a threat and try to hunt him down. Meanwhile, Harry has to figure out how to use his new form to protect himself and his friends. He might meet other Animagi who have similar but different forms, and they could either help or hinder him. Along the way, he could also discover new spells or powers that are related to his Animagus form and use them to fight against the dark forces in the wizarding world.