A really interesting plot could be a time - travel story where a character goes back in time to the era when the Reaper Death Seal was first developed. They could then change the way it was created or how it was perceived, which would have a huge impact on the Naruto universe as we know it.
Another plot idea is to have a character who is not Naruto, perhaps a new OC (original character), inherit the knowledge of the Reaper Death Seal in an unexpected way. This character could then face the moral dilemma of using such a powerful and dangerous jutsu.
Perhaps an unknown hermit living in some far - off place. In many fanfics, there are mysterious characters that pop up with unique knowledge. This hermit could have mastered the Reaper Death Seal long ago and sees Naruto's potential, so decides to teach him.
In this fanfic, Naruto might face some really tough challenges while learning the Reaper Death Seal. He could be in a situation where he has to sacrifice a lot to master it, like maybe losing some of his relationships temporarily. Also, he might have some sort of spiritual journey to fully understand the power of the seal.
A rogue shinobi who has found a way to corrupt the Reaper Death Seal and use it for his own evil purposes. He could be stealing the souls of innocent people instead of using it as a last - resort jutsu like it was intended.
Power and sacrifice are common themes. The death seal is a very powerful jutsu that often requires sacrifice, so many fanfictions explore this aspect. For example, a character might have to sacrifice their own life or something precious to use the seal effectively.
One idea could be exploring how the five pronged seal affects Naruto's chakra in unique ways that were not shown in the original series. Maybe it gives him new abilities or limitations that he has to overcome.
One idea could be Naruto having an encounter with a death - like entity that grants him new and dark powers. He might struggle with the morality of using these powers while still trying to protect his village.
One popular 'naruto reaper death seal fanfiction' is 'The Seal's Legacy'. It delves into the after - effects of the death seal on Naruto's world. Another interesting one could be 'Reaper's Redemption' which focuses on how the reaper aspect in the death seal might have a different agenda than initially thought.
One possible plot idea could be a crossover where Naruto characters gain powers from the DxD universe and have to face a new, powerful enemy. For example, Naruto could learn about the Devil Pieces system and use it to strengthen his allies in Konoha. Another idea might be a story where a character from DxD ends up in the Naruto world and has to adapt to its ninja culture while also using their own unique abilities to help or hinder the existing power balance.
In some 'naruto memory seal fanfiction', the seal might be a tool for an enemy. They could manipulate Naruto's actions by selectively removing or altering his memories. This could create a complex web of mystery and conflict as Naruto tries to figure out what's going on and regain his true self.
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.