Here's a more detailed plot. The character was thought to be dead but was actually in a different dimension. There, they were given a new name and a new purpose. When they come back to the Naruto world, they have to adapt to the changes that have occurred in their absence. They may have to team up with old friends and new allies to face a threat that is bigger than the village itself. They also struggle with whether to reveal their true identity or keep the new name as it represents a new start for them.
It could be Sasuke. Imagine he goes on a long journey and comes back with a new name, having changed in some fundamental ways.
One idea could be that Harry comes back with new magical powers. Since he has faced death, he might have a deeper understanding of magic that was previously unknown. For example, he could have the ability to communicate with the dead more freely, which would help him solve mysteries related to the wizarding world's past.
One idea could be that Harry comes back to Hogwarts as a teacher. He could pass on his knowledge and experiences to the new generation of students. Another plot could involve him returning to solve a new mystery that threatens the wizarding world, something that only he has the skills and knowledge to handle.
One idea could be Naruto going back to the time when the Uchiha clan was still intact. He could try to prevent the massacre by changing certain events or by influencing key people. Another plot could be him traveling back to his own childhood and using his future knowledge to become an even more powerful ninja earlier, like learning advanced jutsus much sooner.
One idea could be Naruto going back in time and preventing the Uchiha massacre. He could use his knowledge of future events to stop Itachi from having to make that tragic choice.
How about the idea of the ninjas from Naruto trying to find a way to reverse the radiation in Fallout 4? They could use their chakra knowledge and skills. Hinata could use her byakugan to detect sources of radiation more accurately. And Naruto could use his positive energy and willpower, which is often associated with his chakra, to try and purify some of the polluted areas.
Sure. Naruto himself is always an interesting character in any Naruto - related fanfiction. His growth and new abilities in this 'second coming' would be fascinating to explore. Also, characters like Sasuke might play an important role. Their relationship could have evolved during Naruto's absence and seeing how they interact upon his return would be cool.
One idea could be that Harry comes back through a powerful ancient magic that was dormant. Maybe a hidden spell in the Forbidden Forest is activated by his friends' strong desire to have him back. Another could be that Death itself gives Harry a second chance because he has unfinished business, like fully ridding the wizarding world of the last remnants of Voldemort's dark magic.
A plot could revolve around Kazehana teaching Naruto about her world's special form of chakra control. Since Naruto has always been eager to learn new ways to improve his skills, this could be an interesting story. He could then use this new knowledge in his own world to fight stronger opponents. For example, Kazehana might show him how to use wind chakra in a more refined and less energy - consuming way.
One idea could be that Naruto discovers a long - forgotten jutsu in an ancient scroll. This jutsu has the power to bring back the dead for a short period. He decides to use it to bring back his parents to seek their advice on how to deal with a new, powerful enemy threatening the Hidden Leaf Village.