Well, it depends on the specific fanfiction. There are countless Naruto fanfictions out there, and each author has their own vision. While the original Naruto is far from a cold assassin, in the realm of fan - created stories, the possibilities are endless. Some fanfictions might do this to add an element of shock or to explore a more edgy and mature version of the Naruto character.
In fanfiction, a cold assassin Naruto would probably be highly solitary. He wouldn't trust easily and would be focused solely on his missions. His jutsu might be more lethal and less about showmanship as in the original series. For example, he could use his shadow clones more as decoys to quickly eliminate his targets without hesitation.
Sasuke could be a likely candidate in a sense. Given his skills as a ninja, his Sharingan which gives him an edge in combat and perception, and his past as a sort of 'rogue' ninja. He could be in a situation where Naruto has to hire him for a special mission that requires his unique abilities. Another possibility is Kakashi. He has a vast array of skills, is very intelligent, and could easily take on the role of an assassin if needed, even if it goes against his normal moral code slightly. He would do it for Naruto's sake.
It could be that his new 'godlike' power has isolated him. People might be either in awe or afraid of him, and he may feel that he can't be close to others as before. So he acts coldly as a defense mechanism.
Jiraiya could be an interesting assassin master. He already has a lot of knowledge and skills that he could pass on to Naruto in a more assassin - like way. His experience in espionage and combat would make him a great fit.
It could be due to a new jutsu he's trying to master that has some side effects on his emotions. Maybe it's a powerful ice - based jutsu that's making him cold in nature as well.
No, not really. Naruto is mainly known for its story about a young ninja's journey, with themes like perseverance and loyalty. While assassin - based fanfiction exists, it goes against the general positive and heroic tone of the original Naruto series that most fans love. So, it's not a widely popular genre within the Naruto fan community.
An OC (original character) could be a godlike assassin. This gives the author complete freedom to create a character with the perfect set of skills, a mysterious background, and a unique personality. They could have powers like teleportation or the ability to control time briefly, which would make them extremely powerful and godlike in the Naruto universe.
One could imagine a fanfiction where Naruto, with his fox - like powers, teams up with an assassin inspired by Altair. Maybe they are on a quest to stop a powerful evil that threatens their respective worlds. They could learn from each other's skills, Naruto teaching Altair - like character about chakra, and the assassin teaching Naruto some stealth techniques.
The fanfiction could focus on how Naruto's ninja skills blend with the Fox Assassin's abilities in an Altair - style setting. They might be in a city full of political intrigue and have to use stealth and combat skills. Naruto could use his shadow clones to gather information, while the Fox Assassin uses his speed and agility.