Edgy SI kun woke up, confused, and seeing that he is not in his own down. He looks for a mirror and sees himself as Naruto a character he hates then punches the mirror. Then he clutches his hand not realising that mirrors can shatter themselves and broken mirror fragments can cut. He cried a bit since SI kun is a normal person not a trained martial artist, or a fighter trained to ignore the pain.
There were no shouts anyway from outside Naruto's apartment complex since nobody would care if a glass dropped or a mirror broke, and it will not really be that loud.
SI kun tried to punch Naruto in the face but he forgot one tiny thing, Naruto was stronger he was and trained in martial arts even as a child, so made a wide swing, and missed. Then he got punched by Naruto back, Naruto as a child is able to jump several feet in the air since he was a child which realistically means he has super strength and knows how to use. SI kun just having the body does not know how to use it.
"Shit! Why is Naruto so strong? Isn't he just a kid like me so how?" SI kun thought to himself. He forgets he never had to use a tiny body to fight before, while Naruto has. Each blow that Naruto gives Si kun hurts and it feels like SI kun's body is breaking.
His ribs ache and throb, SI kun decided to use his last resort and try to take over Naruto's mind.
SI kun tried to be the dominant mind one tiny problem is that he has never have to fight somebody for control over his mind before, thus he has no idea what he is doing, claiming otherwise would just be illogical and unrealistic. He gets socked in the face by Naruto, which breaks SI kun's nose.
SI kun tries to take over Naruto's mind and like Palpatine somehow returning SI kun manages to take parts of Naruto's mind, however he meets massive resistance he also forgets that Naruto a character that he hates, did crazy shit like letting himself get stabbed in the hand to protect Tsunade. So, SI kun lost since he forgets that Naruto already had superior will power from start since he was a child, doing things like letting himself get hurt to protect people, SI kun never did possess such qualities. Nor did SI kun ever had to deal with being an outcast in his own town. Most people who get treated a fraction of what Naruto got in the beginning became usually become school shooters. The fact Naruto never did so is a sign of strength not weakness or cowardice, that SI kun and edge lords like him claim.
Aside from having terrible reading skills and dyslexia, which is no excuse when the Naruto manga is a visually medium.
A proof of that he thinks Naruto is naïve who has no idea how harsh the world is ignoring the fact Naruto raised himself, while SI kun probably never could most people as children cannot. Also, Naruto learned the harshness of the world during the Zabuza arc and learning what a ninja is in his world is to be just a tool for his nation, Naruto dislikes it and vows to change his world (chapter 33). And he does fulfil that promise.
So, SI kun disappears because no form of fanfiction argument will win out in reality and saying so is way to plot armor himself.