One plotline could be Naruto being a transfer student at Hogwarts. He might struggle to adapt to the magic system while also showing off his ninja skills. Another could be Naruto teaming up with Harry Potter to fight a common enemy that threatens both the ninja world and the wizarding world.
Perhaps Naruto is mistaken for a new kind of wizard and has to prove his ninja abilities are different. Or he could be on a quest to find a way back to his own world and in the process, helps Harry and his friends solve a mystery at Hogwarts. There could also be a plot where Naruto's sensei is reincarnated as a Hogwarts professor.
One possible plotline is that Harry is magically transported to the Naruto world and discovers Naruto is in danger from a new, powerful enemy. Harry then uses his magic to fight alongside Naruto and his friends, saving Naruto in the process.
One possible plotline could be that the female Harry Potter, with her new kitsune powers from the Naruto universe, uses them to fight the dark forces in the Harry Potter world in a different way. For example, she might use her kitsune illusions to deceive Voldemort.
One possible plotline could be that the female Harry Potter stumbles upon Naruto's world through some sort of magical accident. She then realizes Naruto's situation and decides to take him under her wing, teaching him about magic in the process. Another could be that she is sent on a mission to Naruto's world for some magical reason and sees Naruto's potential and adopts him as her protege to help him grow stronger both in ninja skills and, with her help, in magic as well.
Another plotline might be that there is a prophecy in the Harry Potter world that only a foreign hero can save Harry. Naruto arrives just in time. He has to learn about the wizarding world quickly while also fending off attacks from the dark side. He could use his shadow clone jutsu to confuse enemies and keep Harry safe.
One possible plotline could be that Harry, after some dark magic influence or a strange accident, starts to show Joker - like behavior at Hogwarts. He might play cruel pranks on his classmates and teachers, using his magic in unexpected and unethical ways.
One possible plotline is that Broly is brought to the Harry Potter world as a result of a powerful spell gone wrong. He initially causes chaos with his strength but then gradually learns about the concept of magic and starts to respect it. Another could be that Broly is a hidden protector of Hogwarts, his Saiyan powers being the ultimate defense against a new dark force that the normal magic in the wizarding world can't handle.
A possible plotline could be that Harry uses his invisibility to spy on Voldemort's followers and gather intelligence for the Order of the Phoenix. This would add an element of mystery and danger as he has to be extremely careful not to be detected.
Maybe Aragorn is summoned to Hogwarts by a powerful spell gone wrong. Once there, he has to figure out how to get back to Middle - earth while also getting involved in the magical world's problems. He could end up teaching the students about non - magical combat skills.
A possible plotline could be that lithium is a key ingredient in a new spell that a young wizard discovers. This spell could be used to combat the dark forces in a unique way. Another plotline might be that lithium is found in a hidden part of the Forbidden Forest and it has some sort of connection to an ancient magic that was long forgotten.
One possible plotline could be that Harry Potter and his friends are magically transported to the NBA world. They then use their magic to enhance their basketball skills and compete against the best players. Another could be that NBA players visit Hogwarts and learn about magic while also teaching the students about basketball.