In a Naruto world fanfic, Killua would bring a whole new dynamic. He has a dark past as an assassin which could either make him a feared or respected figure. His family's training has made him physically and mentally tough. In battles, he could use his electricity - based attacks in creative ways against ninjas. But he would have to learn about things like jutsus and the ninja villages. Also, his relationship with Gon in the HxH world was important for his character development, and in the Naruto world, he might find a similar bond with a fellow shinobi, which could change his perspective on things.
Yes, there are likely some fanfictions out there with such a concept. Fanfiction writers often come up with creative crossovers. You can try searching on popular fanfiction websites like Archive of Our Own or Fanfiction.net.
He could form a rival - like relationship with Sasuke. Both are highly skilled and have a bit of a dark side. They might constantly compete to prove who's better in combat.
I think Midoriya could be his best friend. Midoriya is kind - hearted and always looking to learn, which would appeal to Killua. They could bond over their shared desire to become stronger and protect others.
As I mentioned before, 'lemon' implies adult content which is not suitable for discussion. So, I can't really talk about the characteristics of such fanfics.
No, it's not appropriate. Fanfiction should focus on positive aspects such as character development, new adventures, or exploring relationships in a non - explicit way. Sexualizing a character in fanfiction goes against the spirit of most fandoms which are often family - friendly or at least should be respectful of all ages.
Often, baby Killua in fanfiction is presented as having a strong bond with certain characters from an early age. His loyalty and protectiveness, which are traits that are more prominent as he grows older, are sometimes hinted at in his childhood. He can also be quite endearing, with his small - child clumsiness and his determination to learn new things.