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.
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 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.
I'm not entirely sure as it's a rather specific and perhaps not so common fanfiction concept. It might be about Harry from the Harry Potter series being related in some strange way to Naruto's'splitting' concept, like a clone or some other form of division. But without reading it, it's hard to say for sure.
One great fanfiction could be 'Time's Twist in Slytherin'. In this story, Harry's time travel leads him to be sorted into Slytherin. He has to navigate the complex politics and relationships within the house. It shows a different side of the Slytherin characters and how Harry's presence changes things. He forms unexpected alliances and discovers secrets that were long buried.
Definitely his professors when they were younger. For example, Snape as a student. This would be a strange interaction considering their relationship in Harry's own time. He could also meet Hagrid when he was just starting out at Hogwarts. And there's a good chance he'd run into Sirius and Remus during their school days, and perhaps form new friendships or alliances with them in the past.
In a fanfiction where Harry Potter is on Asgard, he would face many challenges. His magic might not work in the same way as it does on Earth. He'd need to adapt quickly. He could also be seen as a threat by some Asgardians. However, his courage and quick thinking, which he developed in his battles against Voldemort, would help him survive. He might even teach the Asgardians some things about the power of love and friendship, which are important in the wizarding world.
One possibility is that Harry would use this opportunity to change certain events in the past that had a negative impact on the baby or its family. He could also form a special bond with the baby. Maybe he'd introduce the baby to some of his friends from his own time who are also in the past now. This could create a whole new set of relationships and storylines in the fanfiction.
Another possibility is that Harry ends up married to a Muggle he meets in Vegas. This would be really interesting as he has to navigate the differences between the wizarding world and the Muggle world while being married to someone who has no idea about magic at first. It would be a story of discovery and adjustment for both Harry and his new spouse.