It could be about Naruto somehow getting marked by the Shinigami and then being transported to the Gundam universe. There, he might use his ninja skills in combination with Gundam technology. For example, he could use his chakra to enhance the Gundam's power systems or his stealth techniques for sneaking around in Gundam battles.
It could be an evil Gundam pilot who is jealous of Naruto's unique abilities because of the Shinigami mark. This pilot might see Naruto as a threat to his own power and status in the Gundam world and constantly tries to undermine him in battles.
Well, it's quite possible. Naruto has a huge fan base, and many fans like to create unique scenarios. A 'naruto loves shinigami' fanfic could explore interesting relationships and new storylines. However, finding a specific one might take some time as you need to sift through a lot of fanfics. You could start by using relevant tags on fanfic websites.
I'm not entirely sure as it's a fanfic. But it might involve some kind of contract within the Naruto universe related to the Shinigami, like a deal made with a death - god - like entity. Maybe a character has to give something up in exchange for power or knowledge.
In the 'naruto the legendary shinigami fanfic', it could be that Naruto is transported to the realm of the Shinigami. There, he discovers secrets about the Shinigami and its role in the Naruto universe. He may learn about ancient powers or prophecies related to the Shinigami. As he explores this new realm, he meets different creatures and characters. Some might be friendly and help him understand his new situation, while others could see him as an intruder or a threat. Naruto would then have to use his wits and any latent abilities he has to survive and find a way back to his own world, all while dealing with the mysteries of the Shinigami.
In this fanfic idea, Naruto summoning Shinigami captains could be really interesting. Maybe he could summon them to help in a battle against a powerful enemy like Kaguya. The Shinigami captains' unique abilities like kido and zanpakuto skills could turn the tide of the fight. Naruto's own chakra reserves and jutsu combined with their powers would create a very different kind of story dynamic.
Well, in some fanfictions, the Shinigami might save Naruto by using its special powers to reverse a fatal curse or injury. For example, it could extract a harmful entity that was about to kill Naruto from his body.
Maybe the Shinigami uses its special powers to heal Naruto's severe injuries. For example, it could transfer some of its own spiritual energy to Naruto to revive his fading life force.
One possible plot could be that Naruto discovers a hidden realm where Shinigami exist. He meets a particular Shinigami and is immediately drawn to their unique powers and personality. They start to form a bond as Naruto tries to understand the Shinigami's world and how it relates to his own.
One unique aspect is the potential for character development. In a 'Shinigami Naruto Bleach Fanfic', Naruto has to adapt to a completely new world with different rules. This forces him to grow in ways that are different from his original Naruto storyline. Also, the fanfic can explore how the shinigami characters in Bleach view Naruto, an outsider with such different powers. This interaction can lead to unique storylines and character relationships that you wouldn't find in either of the original anime.