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.
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.
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.
In a 'Percy meets Triton at a young age' fanfiction, it could start with Percy being bullied at the beach. He runs into the water to get away from the bullies. Triton, who is observing from afar, is intrigued by Percy's quick thinking to use the water as an escape. Triton approaches Percy and offers to give him the ability to breathe underwater for a short time. They then have a conversation where Triton tells Percy about his own powers and how the ocean can be both a friend and a foe. This encounter plants the seed for Percy's future adventures in the underwater world.
Well, perhaps they could become friends quickly. Bill might introduce Harry to some interesting magical things he hasn't seen before, like some unique creatures. And they could start having little adventures together around the wizarding world.
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.
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.
Well, it could be about Percy learning some unique skills or powers under Fenrir's training. Maybe Fenrir is teaching Percy how to be more in tune with his primal instincts, like better combat skills or a deeper connection to nature.
It could be about Sirius teaching Harry advanced magic skills like Patronus charm. Sirius, being a skilled wizard, might train Harry to be better at dueling and facing dark wizards.
Well, perhaps Percy is being trained in some sort of combat or special skills by Apollo. Maybe Apollo is teaching him archery, which is Apollo's specialty. Percy could be learning to use a bow and arrow in new and creative ways to defeat his enemies.
Well, it could be about Sakura being trained in combat skills. Maybe Orochimaru sees her potential and decides to train her in his unique and somewhat dark ways. He might teach her some forbidden jutsu or special techniques that she couldn't learn elsewhere.