He might be amazed. Naruto is used to his own world and seeing a fan - made interpretation like an AMV fanfiction would be like seeing a new side of his story.
It's highly unlikely. Naruto's world is preoccupied with real - life ninja stuff. Fanfiction and AMVs are products of our modern - day, media - savvy world. There are no computers or the Internet in Naruto's world for him to access such fan - made content.
Well, Naruto might be really confused at first. He's from his own world and an AMV (Anime Music Video) fanfiction is a very modern and fan - created concept. He could be intrigued by the different interpretations of his story or his friends' stories in the fanfiction.
He could also get angry. After all, being misjudged like that is unfair. His anger could lead him to either lash out verbally at Sakura or he could leave the village in a fit of rage, feeling that he is not accepted even by his friends. This could then lead to a series of events where Naruto has to find his own way and Sakura realizes her mistake later on.
Kakashi would be the most perceptive. He'd see how Naruto singing 'Monster' is not just a random act but a way for Naruto to connect with his own fears and insecurities. His friends from the Hidden Leaf Village would overall be proud of Naruto for trying something new and for using the song to share a part of himself that they may not have fully understood before.
Sasuke would likely be deeply affected. He might initially be angry that he couldn't protect Naruto. As Naruto becomes a monster, Sasuke would be conflicted between his desire for power and his loyalty to his friend. He might try to find a way to bring Naruto back to normal so he can have his rival back. Sakura would be heartbroken. She would probably cry a lot and then try to find a medical solution to reverse the transformation. Kakashi would see it as his failure to protect Naruto and would do everything he could to stop the monster Naruto from causing harm while also looking for a way to save him.
Once in Gacha Life, there was a girl named Lily. A group of mean characters would always make fun of her unique outfits. They would laugh and call her 'weirdo' whenever she entered the virtual schoolyard. One day, Lily decided she had enough. She started to focus on making real friends who liked her for who she was. She found a small group that loved her creativity in dressing up her Gacha character. Eventually, those bullies saw how happy Lily was and they stopped their mean behavior.
There was a Gacha Life love story of two characters, Rose and David. Rose was a bookworm and David was a sports enthusiast. They met at a club fair where David was trying to promote the sports club and Rose was looking for a reading club. By mistake, Rose walked into the sports club area and David kindly showed her the way to the reading club. After that, they kept running into each other. David started to borrow books from Rose and Rose would go to watch David's sports games. Their different interests brought them together and they fell in love.
A sad Gacha Life story could be about a character who loses their best friend in the game. For example, they might have planned to build a virtual world together, but then the friend quits playing. It makes the remaining character feel lonely and sad.