One possible plotline could be that Harry has some sort of misunderstanding. Maybe he believes Draco is involved in a dark plot that endangers Hogwarts. So, in a rash moment, he kidnaps Draco to interrogate him. But as he does this, he realizes that Draco might be innocent and then has to deal with the consequences of his actions.
One possible plotline could be that Harry betrays Draco in a duel. Maybe there was some sort of misunderstanding or a secret deal that Harry made with someone else that required him to turn on Draco during the duel. For example, if there was a dark wizard threatening Harry's friends and the only way to save them was to sacrifice Draco in the duel by using a forbidden spell against him.
One possible plotline could be that Harry, through some magical accident or inheritance, comes to own Draco's family manor. Draco is then forced to interact with Harry on Harry's terms to regain his family's pride. Another could be that Harry wins a bet against Draco and the terms of the bet are such that Harry now has ownership over Draco's time, making Draco do tasks for Harry.
One possible motive could be revenge. Maybe Draco feels that Ginny or the Weasleys have wronged him or his family in some way. For example, if he blames Ginny for getting Harry Potter on their side all the time which has made things difficult for the Malfoys at Hogwarts. Another motive could be related to power. He might think that by kidnapping Ginny, he can gain some sort of leverage over the Order of the Phoenix or Dumbledore's side. It could also be out of jealousy. If he has some unspoken feelings for Ginny but she's always with Harry, he might kidnap her in a fit of jealous rage.
Another plot could involve a sort of magical exchange. Orochimaru, being a master of some dark and strange jutsu in his own world, might offer to teach some of his knowledge to certain dark wizards in the Harry Potter world in exchange for something valuable. Harry Potter and his friends would have to prevent this knowledge transfer as it could tip the balance of power towards the dark side in their world. They might need to seek help from some of the more powerful and wise wizards like Dumbledore to outwit Orochimaru.
Another plot could involve Medusa being a part of a long - forgotten magical mystery that is somehow related to Harry's destiny. Harry, with his inquisitive nature, starts to research about her. As he gets closer to the truth, he has to face the danger of being turned to stone. But through his courage and the help of his friends, he manages to break the curse on Medusa, and in return, she helps him in his fight against Voldemort.
Another plot could involve Draco actually knowing some secrets about the Horcruxes that he initially doesn't want to share with Harry. But as the danger of Voldemort's power growing becomes more and more real, he realizes he has to help. So, during the hunt, Draco gradually reveals bits of information that he has, which helps Harry in unexpected ways. This could lead to a redemption arc for Draco, as he goes from being on the side of the Death Eaters in a way to actively working against Voldemort by assisting Harry.
One possible plotline could be that they start to secretly help each other with their studies. For example, Draco might be struggling with a certain type of magic that Harry is good at, like Patronus Charms. In secret, Harry could give Draco some tips. Another could be that they team up to solve a mystery in Hogwarts that no one else is aware of. They might discover a hidden chamber or a secret spellbook together. They would have to keep their friendship a secret because of the rivalry between Gryffindor and Slytherin. Their friendship could also be tested when their respective houses are in competition, but they still find ways to support each other on the sly.
One possible plotline could be that Sasuke has been misled by some false information. Maybe he believes that the female Naruto is in some way a threat to Konoha's future. So he kidnaps her to keep her away from the village. However, as he spends time with her, he realizes his mistake and they end up working together to clear up the misunderstanding.
One possible plotline could be that Uncle Matthew Potter has some long - lost magical power or artifact that the main characters need to find. This could lead them on an adventure through different parts of the wizarding world. Another plot could involve him having a secret connection to a dark wizard from the past, and the story could be about uncovering this connection and dealing with its consequences.
Perhaps Harry discovers that he has basilisk blood in him. This could change his abilities and how others view him. He might face discrimination from some in the wizarding world who fear the basilisk's power, while others might see him as a potential weapon against Voldemort. The plot could revolve around Harry coming to terms with this new aspect of himself.