One common theme is self - discovery. When Naruto is alone, he often has time to think about who he is and what he wants. Another theme is inner strength. He has to rely on his own abilities and not depend on others. For example, in many fanfictions, he overcomes great difficulties alone using his own skills.
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.
" I Walk Alone on the Cold Street " was a song sung by Zhang Youqian. The lyrics of this song described a person walking alone on a cold street, feeling lonely and lonely. The song expressed the memories and longing of past love, as well as the expectation and confusion of the future. The lyrics of this song were " The wind blows gently on my face, the rain soaks my clothes, I walk alone on the cold street, who else will accompany me?"
He could meet an old enemy who has also changed after the war. This enemy might now be in a similar situation of being alone and they could form an unexpected bond as they understand each other's isolation.
He might meet an old sage who has been living in seclusion near the village. The sage could see Naruto's loneliness on his birthday and offer him some ancient ninja knowledge.
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.
Maybe an ancient evil ninja who was sealed away long ago but has now been released. This antagonist could have powers that nullify any communication or summoning jutsu, forcing Naruto to fight alone. He would be extremely powerful and know many forgotten and deadly jutsu.
In a 'naruto fights alone fanfiction', it could be that Naruto is on a mission in a foreign land where he has no support. The local ninjas are all against him for some reason. He has to use his Nine - Tails chakra in a more discreet way as he can't afford to go all - out and draw too much attention. He might befriend some local animals or spirits who help him in a more indirect way, like giving him information about the enemies' weaknesses.
One common theme is self - discovery. When Naruto is alone, he has more time to think about who he is. He might question his purpose in life, like whether he's just a tool for fighting or if there's more to him.