Rukia could also be a main character in this crossover fanfiction. Her knowledge of the Soul Society and her own unique powers could add a lot to the story. She could form an interesting relationship with some of the more robotic - like characters from the Fleet of Fog, perhaps teaching them about the concept of souls and the afterlife.
Sasuke could also be a main character in this fanfiction. His brooding and powerful nature would add a different dynamic to the story. He might have a more conflicted relationship with the Fleet of Fog compared to Naruto. And perhaps a female character from the Fleet of Fog, like a skilled navigator or strategist. She could provide a fresh view and have some interesting interactions with the Naruto characters, whether it's in terms of friendship or rivalry.
I think Neville could be an interesting main character in this crossover. He has grown so much in the Harry Potter series, and his knowledge of plants could be used in some unique ways against the Fleet of Fog. For example, he could use some magical plants to either hide Hogwarts from the Fleet of Fog's sensors or use them as a form of defense. From the Fleet of Fog, a young and curious engineer could be a main character. They would be fascinated by the magic and would try to figure out how to incorporate it into their technology. Ginny Weasley could also be a main character, with her strong will and magical abilities.
One interesting concept could be the interaction between the unique powers in 'Bleach' and the technology or abilities within the 'Fleet of Fog'. For example, how would a Soul Reaper's zanpakuto fare against the advanced weaponry of the Fleet of Fog ships.
Adaptation is a major theme. The characters in the fleet of fog have to adapt to the new rules and situations in the crossover. Also, discovery is common. They discover new powers, new species, or new technologies during the crossover. It makes for very interesting storylines as they figure out how to deal with these new things.
Well, perhaps the 'Fleet of Fog' enters the wizarding world and the wizards initially mistake them for some new kind of dark magic creatures. Harry and his friends then have to figure out what they are and find a way to either make peace or drive them away. The wizards could use their magic to try and understand the technology of the Fleet of Fog, like Ron trying to figure out how their engines work with a simple 'Engorgio' spell on some of the parts to see what happens.
Well, in this 'naruto fleet of fog crossover fanfiction', a great concept might be the cultural clash. The ninja world of Naruto has its own set of values, traditions, and power systems. When it crosses over with the Fleet of Fog, which likely has a very different military - based and perhaps more technology - focused culture, there could be a lot of interesting interactions. Characters from both sides would have to learn to understand and adapt to each other's ways, which could lead to some really engaging storylines.
One great 'fleet of fog crossover fanfiction' story is 'The Fog's Encounter'. It combines elements in a really interesting way. The characters from different parts of the fleet of fog universe interact in unexpected scenarios, which makes it a thrilling read.
A possible main antagonist could be Aizen from 'Bleach' who somehow gains the ability to control the powers from Lucy's world as well. He could use this newfound power to try and take over both the Bleach universe and Lucy's world. His cunning and powerful abilities would make him a formidable foe for Lucy and the Bleach characters to face.
Engineering characters from the Katana Fleet can also be great inclusions. They can use their technical knowledge to help or hinder the situations in the crossover. Maybe they have to fix a crucial piece of technology from the other series' world, or they might accidentally cause a problem while trying to adapt their own technology to the new environment.
Itachi and Toshiro Hitsugaya could have a very deep and thought - provoking interaction. Itachi, with his complex past and his sacrifices, might make Hitsugaya reflect on his own sense of duty. Meanwhile, Hitsugaya's strict sense of justice could make Itachi question some of his own actions. Also, Hinata and Orihime could bond over their shyness and their strong feelings for their respective love interests.