Maybe in this fanfiction, a magical accident during a battle turns Harry into a weapon. He has no control over it at first. The weapon form could be something like a powerful sword. Voldemort then tries to use Harry (in weapon form) to defeat the Order of the Phoenix. However, Harry's willpower is so strong that he starts to fight against the transformation from within and slowly gains some control over his new form.
In the fanfiction, an old and evil magic artifact might be the cause. Harry touches it accidentally and is transformed into a weapon. He might be turned into a crossbow that shoots magic - infused arrows. Dumbledore, suspecting something is wrong, starts an investigation. Meanwhile, Harry, now a weapon, is passed around in the wizarding underworld. Some want to use him for evil deeds, while others want to study him to figure out how to reverse the transformation.
One possible plot could be that a dark wizard uses a powerful and forbidden spell on Harry. This spell alters his very essence and turns him into a weapon. He then becomes a tool in the dark wizard's hands to attack Hogwarts. But his friends, like Hermione and Ron, notice the change and try to find a way to reverse the spell. They search through ancient books in the restricted section of the library and finally discover a counter - spell.
In this fanfiction, it could be that a powerful enemy from another dimension arrives. This enemy has the ability to turn living beings into weapons. They see Naruto as a prime target because of his strong chakra. Once turned into a weapon, Naruto might be used to break through the defenses of Konoha. His friends then have to find a way to reverse the transformation, which could involve a long and dangerous journey to find a special antidote or a powerful jutsu.
Well, perhaps he could use his new dragon form to fight against Voldemort in a very unexpected way. He might be able to breathe fire on the Death Eaters and protect Hogwarts more effectively.
In this fanfiction, it might be that a new and mysterious potion was accidentally spilled on Harry. As a child, he'd be super cute and all his friends would be really confused. Hermione would probably immediately start researching ways to reverse the spell. Ron, on the other hand, would be a bit more clumsy in dealing with this new young Harry. And Harry himself might have a lot of fun exploring Hogwarts in a new way, with the perspective of a child but the knowledge of an older wizard.
Perhaps the fanfiction focuses on a heist at Gringotts to steal this special weapon. The characters might face all kinds of obstacles, like the complex security systems in Gringotts, which include things like the dragon guarding the vaults and the magical spells protecting the treasures. They would need to use their unique skills and knowledge of magic to get past these barriers.
Maybe it starts with a strange magical experiment gone wrong in Hogwarts. Harry is curious and gets too close, and suddenly he's a baby. The story could then focus on how the teachers, especially Dumbledore, deal with this situation. They might try to figure out if this is a new form of dark magic they haven't seen before. And Harry, as a baby, would have no memory of who he is, so it could also be about his friends trying to make him remember bits of his past life.
Maybe Harry is turned into an elf by a misfired spell. Then he has to deal with his new small size and pointy ears while still trying to attend Hogwarts classes. He might face challenges like fitting into his regular robes or being taken less seriously by some students.
Well, perhaps Harry could be a weapon that has the power of his magic from the Potter world. He might be used by a Soul Eater character to fight against evil souls. Maybe his wand could transform into a more weapon - like form in the Soul Eater world.
Well, one possible plot could be that her friends have to take care of her as a baby. Harry and Ron might struggle to figure out how to keep her safe and fed. They could search for a way to reverse the spell that turned her into a baby.
Well, perhaps the plot could involve the other characters having to take care of baby Kagome. Inuyasha might be really confused at first but then grow protective. Sango and Miroku could help out too, trying to figure out how to turn her back while also making sure she's safe and healthy.
One possible plot could be that Ash, as a female, has to face different challenges in the Pokémon world. For example, some trainers might underestimate her at first. But she uses her knowledge and skills to prove them wrong. She might also form different relationships with her Pokémon. Maybe her Pikachu would be even more protective of her in this new form. And she could have unique adventures that are different from her male self's, like being more involved in Pokémon contests due to the perception that female trainers are more into that aspect of the Pokémon world.