The plot might involve Grindelwald coming to Britain to recruit followers for his cause. Phosphene could be a symbol or a power source that he believes will help him achieve his goals. Tom Riddle, being a Slytherin and already showing signs of his dark nature, is approached by Grindelwald. However, Tom has his own plans. He wants to use Grindelwald's knowledge and Phosphene's power to rise to the top on his own terms. So, he plays a double - game, pretending to be a loyal follower while secretly plotting against Grindelwald.
A great plot could be centered around a prophecy in Britain that involves Grindelwald, Phosphene, and Tom Riddle. Grindelwald believes that by controlling Phosphene, he can change the prophecy to his advantage. Tom Riddle, on the other hand, has heard about the prophecy as well and wants to use it to his own benefit. Phosphene, which might be a sentient magical being, has its own will and doesn't want to be used by either of them. The fanfic could then follow the struggle between these three as they each try to manipulate the situation according to their own desires.
A fanfic like this might explore the dark magic that Grindelwald wields in the British wizarding world. Phosphene could be a new magical creature or a spell that has some connection to the events. Tom Riddle, being the cunning and ambitious young wizard, might see Grindelwald as a sort of role model, at least in terms of achieving great power. The story could show how the different magical elements and characters interact and how their fates are intertwined.
One possible plot twist could be that Tom Riddle kidnaps Harry not for the typical reasons like revenge or to gain power over the wizarding world. Maybe he discovers that Harry has some hidden knowledge about a long - lost magic that he wants for himself. Another twist could be that while kidnapped, Harry manages to find a way to get into Tom Riddle's mind and discovers his deepest fears, which he then uses to his advantage to try and escape. It could also be that there are other dark forces at play that Tom Riddle is actually trying to protect Harry from, in his own twisted way, by taking him away from the wizarding world for a while.
Perhaps in this fanfic, the apartment is a magical place that serves as a crossroads between different timelines. Tom Riddle stumbles into it while Hermione is already there studying some ancient magic. They are forced to co - exist in this small space. Tom is initially hostile, but Hermione uses her wits to keep him in check. As they interact more, they begin to understand each other's perspectives on magic, and a strange bond forms between them that could potentially change the course of the wizarding world.
The plot could center around a ballet competition. Tom Riddle, with his natural ambition, is determined to win at all costs. Hermione, on the other hand, is there to experience the beauty of ballet. Their paths cross, and they start to influence each other. Tom might learn about the value of fair play from Hermione, while Hermione might understand the depth of Riddle's past traumas that drive his cutthroat nature.
In fanfiction, Merope Gaunt and Tom Riddle Sr's story could be a tale of redemption. Maybe Merope realizes the wrong she has done in using a love potion on Tom and tries to make amends. She could attempt to win his love genuinely, without the use of magic. This would show her growth as a character and add a new layer to their relationship.
In a 'Grindelwald Adopts Harry' fanfic, Grindelwald could be seeking to create an heir of sorts. He adopts Harry when he is very young. Grindelwald might expose Harry to a world of magic that is different from what he would have known at Hogwarts. Harry could be taught magic that is more about power and control. However, as Harry gets older, he might discover the truth about Grindelwald's dark deeds and his plans for the wizarding world. This could lead to a great internal struggle within Harry as he has to choose between the man who raised him and what he believes is right for the wizarding community as a whole. There could be a lot of drama as Harry tries to find his place and figure out his true identity in this new and rather dark scenario.
One possible plot could be that Harry, using his knowledge of love and friendship, tries to teach Tom about the power of positive emotions. He might show Tom how his own journey was shaped by the love of his friends and family, in contrast to Tom's more solitary and power - hungry path. Maybe Harry takes Tom to Hogwarts in a time - travel like scenario and shows him the true meaning of the houses, not just the pursuit of power within Slytherin.
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 possibility is that Harry, having seen the dark path Tom Riddle took, decides to take him in early. He might teach Tom about love and friendship, things he lacked growing up. Harry could introduce Tom to the wizarding world in a more positive light, showing him the joys of Hogwarts and the value of good relationships, thus preventing him from turning into Voldemort.
One possible plot could be that Harry discovers some long - lost secrets about Tom Riddle's early days at school. Maybe he stumbles upon a hidden diary that reveals Riddle's true motives even before he became Voldemort. This could lead to Harry trying to prevent some of the dark magic that Riddle was starting to dabble in from ever happening.