Another interesting plotline could be that in his past life, Harry had a relationship with a character that is very different in his current life. This could create a lot of emotional turmoil and interesting character dynamics as he tries to reconcile his past feelings with his present situation.
Obviously, Harry himself is the central character. Hermione would likely be involved as well. She could be the one who helps Harry research and understand his past - life memories. Maybe she finds ancient texts that give clues about what Harry is experiencing.
One interesting concept could be how Harry's past - life memories influence his relationships. For example, if he remembered a past life as a powerful wizard, he might be more confident in dealing with his friends or enemies. Another concept could be how these memories affect his understanding of magic. Maybe he discovers new spells or magical theories from his past - life knowledge. Also, it could change his view on the wizarding world's history and his place in it.
One interesting concept could be how Naruto's past life memories change his relationships. For example, if he remembered being a great warrior in his past life, he might approach his training with Sasuke differently, seeing it as more of a friendly rivalry between two equals from different lifetimes. Another concept could be how his past life knowledge affects his view of the ninja world. Maybe he has memories of different forms of chakra usage that were lost in the current era, which could lead to him revolutionizing the way ninjas fight.
In this fanfic, a really cool plot could be that Harry has been secretly communicating with other wizards outside of his family through a magical object. They've been planning his escape for a long time. They send him a special charmed item, like a bracelet that can turn him invisible at will. He uses this to his advantage and slips away from his family during a chaotic moment, like when they're having a big argument. Then, he follows a series of clues left by his new friends to reach a safe haven, a hidden magical community where he can finally be free and learn more about his true potential.
One possible plotline could be that Harry discovers a powerful time - traveling spell in his third year at Hogwarts. He decides to use it to go back in time and save his parents. Along the way, he has to face challenges like avoiding detection by the time - turner regulations and dealing with dark wizards who are also lurking in the past.
One interesting plotline could be Harry using his knowledge from his first life to prevent certain tragedies. For example, he might be able to save Sirius Black much earlier by being more cautious about the events at the Ministry of Magic. Another could be him changing his relationships with his classmates. He might befriend Draco Malfoy in a different way, perhaps by reaching out to him and understanding his family situation better, which could lead to a very different dynamic at Hogwarts.
One interesting plotline could be how the twin sister helps Harry deal with the challenges at Hogwarts in a different way than his friends. Maybe she has a unique magical ability that aids them in fighting the dark forces.
One interesting plotline could be Harry's parents' time at Hogwarts. Maybe exploring how they formed their friendships and dealt with the early signs of Voldemort's rise. Another could be about the Marauders' adventures that were not fully shown in the original books, like their secret pranks and how they influenced the Hogwarts of that time.
One interesting plotline could be Harry's adventures in the afterlife realm where he has to deal with different types of souls. Maybe he meets some souls with unfinished business and tries to help them move on.
Well, one possible interesting plotline could be Harry teaming up with the Autobots to fight a common enemy. Maybe there's a powerful Decepticon that threatens both the wizarding world and the Autobots' home planet, and Harry's magic combined with the Autobots' technology is the key to victory.