There's a possibility that it's a former Soul Reaper who has retired. This ex - Soul Reaper notices Ichigo's natural talent for sensing spiritual energy and takes it upon himself to train Ichigo, passing on his skills and knowledge about Soul Reaper techniques.
Maybe an old and wise spirit that Ichigo encounters. This spirit sees great potential in Ichigo and decides to train him in the ways of the spiritual world, teaching him about the balance between the living and the dead.
In this fanfiction, Ichigo's training at a young age might be a result of a premonition of a great danger to come. A powerful shinigami takes him under his wing and starts training him in combat skills against Hollows. The training is intense, with Ichigo learning how to use his reiatsu more effectively, and also learning about the different types of Hollows and how to counter them.
There's a possibility that his trainer is a self - taught expert. This person could have learned about pistols through years of exploration and practice. They see potential in Harry and take it upon themselves to train him, sharing their unique and unorthodox methods of pistol training with Harry.
There's a chance it could be a powerful house - elf. House - elves are known for their own brand of magic, and one particularly rebellious or enlightened house - elf could decide to train Harry in magic that is more about stealth and quick - thinking. After all, house - elves have to be very sneaky to avoid detection by their masters most of the time, and this kind of skill could be very useful for Harry in his battles against Voldemort.
Maybe it's a former Death Eater who has seen the error of his ways. He wants to atone for his past sins by training Harry to defeat Voldemort. He has inside knowledge of the dark side's tactics and uses this to make Harry a more formidable opponent.
His friends like Rukia or Chad could come to his rescue. They care about Ichigo deeply and would surely try their best to find and save him.
I think his family would be the first to help. His sisters could bring him cold compresses to reduce the fever, and his father would use his medical skills. And from the Soul Society, Renji might come to check on him, as he and Ichigo have a sort of friendly rivalry. He would want to make sure Ichigo gets better soon so they can have their next sparring match.
Yes, there are likely to be such fanfictions out there. The idea of Naruto being trained by Ichigo combines two very popular anime characters from different series. Fanfiction writers often come up with creative crossovers like this. You can try searching on major fanfiction platforms to find specific works.
Naruto fans who like to explore alternative storylines would be interested. People who are fans of Sakura and want to see her in new situations, like being trained by a powerful character like Madara.
Maybe it's a member of a long - lost ninja clan. This clan member could have some special skills and knowledge that they want to pass on to Naruto. They choose to train him in secret to protect their clan's secrets from falling into the wrong hands.
It could be an unknown ninja from a far - off village who specializes in Storm Release. This ninja might have heard of Naruto's potential and decided to train him.