He might be shocked. In the fanfic, if he sees things like his friends' future achievements or the new threats that emerge, it would surely startle him. For example, if he discovers that one of his friends has a family of their own and has become a great leader in the village, he would be proud but also a bit surprised at how much has changed.
With his usual determination. Naruto has always been one to face difficulties head - on. So, even if he's shocked by what he sees in the fanfic's future, he'll likely try to find solutions immediately.
I don't know who xqc is in this context without more details. It could be someone's username, a streamer, or just a name given to a character in a particular situation.
I'm not entirely sure specifically what 'xqc reacts to neuro story' is about without more context. It could be that xqc, perhaps a person or a character, is reacting to a story that has something to do with the neuro (which could potentially refer to neuroscience, neural networks, or something related to the nervous system in a more general sense).
One popular 'Overwatch Reacts' fanfiction could be the ones where the Overwatch characters react to different timelines or alternate universes. For example, they might react to a world where the Omnic Crisis was never resolved. Another could be their reactions to new heroes joining the team. It's all about exploring the characters' personalities through these reaction scenarios.
A Naruto fanfiction can be sad when it delves into the sacrifices Naruto has to make. He gives up so much of his personal life and relationships for the sake of the village and his friends. If a story highlights how he loses his close friends, like Sasuke in some darker interpretations, it can be extremely sad. Additionally, if it shows Naruto being misunderstood by the people he's trying to protect, that also adds a layer of sadness. For instance, if the villagers still don't trust him despite all his efforts, it can be a very tragic situation for Naruto.
Well, Kurama's sad story in Naruto Shippuden is complex. He was feared by the villagers in the Hidden Leaf because of his power. When he was sealed into Naruto, he was angry and tried to take over Naruto's body multiple times. His past was filled with being hunted and then trapped. It wasn't until he started to understand Naruto's will and dreams that he began to change. Naruto's unwavering determination and kindness towards him slowly melted his cold heart.
One sad story in Naruto is about Sasuke. His entire clan was massacred when he was young. He had to live with this trauma and the thirst for revenge. He left his friends in Konoha, like Naruto who considered him a brother, to seek power from Orochimaru. This led to a long separation and many battles between them.
Some Tumblr blogs are dedicated to sharing and promoting AOT fanfictions, including the reacts ones. You can search for relevant tags like #AOTreactsfanfiction on Tumblr. Also, Reddit has some subreddits dedicated to AOT. You might be able to find links to AOT reacts fanfictions in the posts or comments there.