It could start with Harry's sacrifice in his own world being so powerful that it breaks the barriers between universes. He arrives in Naruto's seal disoriented at first. Then, he realizes he can communicate with Naruto through the seal. Harry could start sharing his knowledge of different types of magic with Naruto, which Naruto could then adapt into new jutsu concepts. They could form a sort of symbiotic relationship where Harry helps Naruto become even stronger while Naruto gives Harry a new purpose and a place to exist in this strange new world.
Well, perhaps in the moment of Harry's death, a powerful dark magic from the Harry Potter world collided with a strange space - time anomaly in the Naruto universe. This catapulted his essence into Naruto's seal. Inside the seal, Harry could be a source of new wisdom for Naruto. He could teach Naruto about things like loyalty and sacrifice from his own experiences. And he might also gain some of Naruto's positive traits, like his unwavering determination, which could help him in his new 'afterlife' within the seal.
He could develop the ability to use chakra. Since he's in the Naruto universe now, he might figure out how to manipulate chakra using his magical intuition. Maybe he could combine his Patronus charm with chakra to create a new kind of protective shield. Also, he could learn to move at high speeds like Naruto characters do, which would be a new ability for him considering he was mainly using apparition in his own world.
One way this could unfold is that Naruto and Tenten are on a mission together. They are suddenly attacked by a powerful and unexpected enemy. Naruto, being the selfless hero he is, sees the enemy about to strike a fatal blow on Tenten. He jumps in front of her without hesitation, taking the full brunt of the attack. His last moments could be him telling Tenten to keep fighting and protect the village.
The interaction between Harry's ghost and Naruto's seal in this fanfiction could be really complex. Harry's ghost might initially be confused when it ends up near Naruto's seal. It may not understand the nature of the seal at first. However, as it observes, it might notice the flow of chakra within the seal. If Harry had some knowledge of sealing magic in his own world, he might try to compare it to what he sees in Naruto's seal. His ghost could also potentially be a catalyst for some change in the seal. Maybe it causes the seal to react in a way that it has never reacted before, which could either be a good or a bad thing depending on the context of the fanfiction.
In this type of fanfiction, Naruto's death while protecting Hinata could be the turning point of the whole story. It could cause a shift in the power dynamics of the village. Hinata, on the other hand, would be deeply affected. She might become more withdrawn at first, but then gradually find the strength within herself. His death could also inspire the younger generation to be more like Naruto, always ready to sacrifice for the ones they love.
One consequence could be that it disrupts the balance of chakra within the seal. This might lead to Naruto having some issues with his power control or even cause the seal to weaken or malfunction.
Well, Naruto could start his journey by accidentally stumbling upon a zanpakuto in a strange dimension. Maybe he's on a mission and gets sucked into a portal that leads to the Soul Society. There, he discovers the power of the zanpakuto and becomes fascinated. He might start training with the Shinigami to understand and master the use of the zanpakuto. Since Naruto is known for his determination, he would quickly adapt to the new fighting style associated with the zanpakuto.
One possible storyline could be that Naruto is faced with an overwhelmingly powerful enemy that he realizes can't be defeated any other way. So, in a selfless act, he decides to use the Reaper Death Seal. This would be a very tragic end for Naruto as he has so many friends and a family to live for. His death would likely send shockwaves through the Hidden Leaf Village and among his friends like Sasuke, Sakura, and Kakashi. They would be devastated, and it might also lead to a power vacuum in the village, causing all sorts of political and social unrest.
If Harry is stuck in Naruto's seal in fanfiction, he could potentially discover new forms of energy or power. Since he's used to magic, being in the seal might expose him to different types of energy like chakra in a very direct way. He could also make friends with the entities inside the seal, who could teach him things about Naruto's world that he would never have known otherwise. This could give him an edge when he finally gets out of the seal and has to interact with Naruto and the others.
Well, if Harry was the son of Supergirl in fanfiction, he might have a really hard time fitting in at first. In the wizarding world, magic is the norm, but he would have these other powers that are completely different. He'd probably have to keep his Kryptonian side a secret, at least until he knew who he could trust. And his upbringing would be so different from the normal wizard upbringing. Instead of just learning spells, he'd be learning how to control his superpowers too.
One way the story could unfold is that Fem Harry, with her magical abilities, could be mistaken for a new kind of enhanced being by the Avengers. Maybe she appears in their world through some magical portal mishap. She could initially be seen as a threat, but then as they learn about her and her fight against the dark forces in her own world, they start to respect her and work together. For example, her spell - casting could be useful in battles against powerful enemies like Thanos, providing a different kind of offensive and defensive power.