Well, a possible plot idea is that Naruto, reborn as Tsuna, tries to change the future of the Tsuna's world. He could use his knowledge from his previous life in Naruto's world to prevent some of the darker events that were supposed to happen in Tsuna's world. Maybe he could also introduce some of the ninja concepts like the ninja way into Tsuna's family and friends, which would change their way of thinking and acting.
One interesting plot could be Naruto using his ninja skills in the world of Tsuna. For example, he might use his shadow clone jutsu to help Tsuna deal with multiple threats at once. Another could be Naruto teaching Tsuna some of his unique chakra control techniques which could enhance Tsuna's own combat abilities in his world.
Well, perhaps in this fanfiction, Harry, now Tsuna, has visions of his past life at Hogwarts during his battles in the KHR world. These visions give him an edge as he can draw on the spells and strategies he used against Voldemort to fight his new enemies. Also, his relationship with Reborn could be really interesting. Reborn might be intrigued by Tsuna's strange bursts of knowledge and skills that seem to come out of nowhere, which are actually remnants of Harry's past magical training.
A really interesting plot could be that Tobirama is reborn as a non - ninja, but still has his chakra control abilities. He has to find a way to use his skills secretly while living a normal life at first. As he discovers more about the world he's in, he starts to influence the ninja world from the outside, creating a whole new dynamic in the story.
Another plot could be that Nagato is reborn with new powers. With these powers, he aims to unite the different ninja villages in a more peaceful way than before. He could start by building alliances through diplomatic means and by using his powers to solve common problems, like natural disasters or threats from outside the ninja world.
Well, a plot could revolve around them building their dream home. Haru might have very specific ideas about how the home should look and feel, while Tsuna is more concerned about the security aspects. They have to compromise and work together to create a home that is perfect for both of them. This could also involve some comical moments when contractors don't understand their requests or there are unexpected problems during construction.
One interesting plot idea could be the main character having a unique ability that changes the course of the Naruto world. For example, being able to control time in a limited way during battles, which would give a new twist to the combat scenarios we know from the original Naruto.
A really interesting plot would be Naruto, reborn as Sasuke, trying to prevent the events that led to Sasuke's departure from Konoha in the first place. He would use his knowledge of the future and his Naruto - esque determination. He might also struggle with Sasuke's memories and emotions, which could create internal conflict. For example, when dealing with Orochimaru, he would have to fight the urge to follow Sasuke's original path while also trying to outwit Orochimaru with his own Naruto - like wits.
Another plot could involve Hibari getting involved in the Akatsuki's plans. Maybe he initially misunderstands their motives and gets caught up in their activities, only to later realize their true nature and try to stop them. This would bring a new dynamic to the Akatsuki's story.
One idea could be that Harry Potter is reborn in the Naruto world as an Uzumaki. He could use his magical knowledge in unique ways, like using magic to enhance his chakra control. Maybe he creates new jutsu that combine magic and chakra, such as a spell - enhanced Rasengan.
Another plot could be Tsuna traveling back to a time when his father was still around. He could get to know his father better and learn some hidden family secrets. This would not only strengthen their relationship but also give Tsuna an edge in his future as the Vongola boss. He might learn about some special powers or techniques that his father knew but never got to pass on to him in the original timeline.
Naruto might become a bit more reserved at first. Since Tsuna's world is different from Naruto's, he'd have to adapt. But his core of being kind - hearted and determined would remain. He might be more cautious as Tsuna initially isn't as bold as Naruto was in his own world.