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.
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.
In a fanfiction where Naruto is trained by Ichigo, there would be a lot of changes. Naruto's chakra control could be improved in new ways under Ichigo's training. Since Ichigo is used to dealing with spiritual power, he might help Naruto understand the flow of energy in a different manner. Moreover, Naruto could learn about Ichigo's way of facing powerful foes without hesitation. This could make Naruto even more fearless in combat, and his Rasengan or other jutsu might be enhanced with new elements inspired by Ichigo's powers.
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.
One possible plot could be that Naruto, seeking to gain new powers, somehow ends up in Ichigo's world. Ichigo, seeing Naruto's potential, decides to train him. Naruto then has to adapt to Ichigo's training methods which are different from what he's used to in Konoha. As he trains, he starts to combine his ninja techniques with Ichigo's Soul Reaper powers, becoming a truly godlike figure.
Well, ancient Ichigo in a strong Ichigo fanfic is appealing because he often represents a more primal and powerful version. His ancient power can add a sense of mystery and a connection to a long - forgotten past. It gives the character a depth that the normal Ichigo might not have, and it can open up new storylines and character developments.
Naruto's abilities would change significantly. Ichigo has unique spiritual powers, and through his training, Naruto might develop a form of 'spiritual chakra'. His ninjutsu could become more powerful as he combines the new understanding of energy with his existing chakra control. Also, Naruto's combat strategy would shift as he learns from Ichigo's more direct and aggressive fighting style.
Orihime is a no - brainer. She'll be by his side constantly, using her Soten Kisshun to heal his injuries. But also, Yoruichi could play a role. She's wise and experienced. She might teach Ichigo some new techniques or ways to regain his energy faster. And let's not forget Kisuke Urahara. He's full of tricks and knowledge. He could provide Ichigo with some special items or training methods to help him recover more effectively.
Kisshu and Ichigo are likely characters from a particular anime or manga series. They are the main focus in this fanfiction where the situation of pregnancy is involved.