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.
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.
It could be related to some sort of external influence, like a curse or a dark chakra that has infected him. This could be slowly changing his personality from the warm - hearted Naruto we know to a cold - hearted version. For example, if there was a powerful enemy who placed a curse on him that targeted his emotions.
One characteristic could be a cold - hearted or aloof main character. In Naruto yaoi fanfic, this character might be distant at first, creating a sense of mystery. For example, a character like Sasuke could be portrayed as very cold towards others, especially in a yaoi relationship context.
Good cold Naruto fanfiction often has a vivid description of the cold environment. For example, it might detail how the characters' breath turns to mist, or how the ice forms on their weapons. Also, it should tie in the cold with the Naruto universe's themes like friendship and growth. Naruto might face challenges due to the cold that test his limits and relationships with others.
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.
The 'naruto is ice cold fanfiction' could potentially be about Naruto being physically cold, like he has some sort of ice - based power that is affecting his body temperature and his overall demeanor. Or it could be a metaphorical coldness. Maybe he has lost his hope or has become jaded in this fanfiction's storyline. It could also be a unique spin on the Naruto universe where the normally warm - hearted Naruto is now 'ice cold' to create a contrast with the original character's traits.
She might be confused at first. Sakura is used to Naruto being friendly and always there for her, so his coldness would be unexpected. She may start to question what she has done wrong.
Well, Naruto uses his ninja skills. He could find a sheltered spot to train in, like a cave, which offers some protection from the cold wind. Also, he may have learned some survival techniques. He could make warm drinks from local plants or animals if it's in a more wilderness - like setting. And of course, his physical strength and endurance play a big role. The more he trains, the more his body can adapt to the cold.