Madara Uchiha could also be a likely cause. If he somehow managed to return or had a long - planned scheme that involved breaking Naruto's sanity. He was a very powerful and devious foe who could use his knowledge of the ninja world and its powers to target Naruto's mental stability.
It depends on your perspective. To some extent, Pecola shows signs of mental instability at the end, but it's also a reflection of the harsh circumstances she's been through and the lack of support around her.
No, Betty isn't insane. She's often shown as a kind, friendly, and sensible person in the comic series. Her actions and behaviors are typical of a normal character.
Well, you can start by looking on fanfiction.net. There are often a lot of unique takes on Percy there. Some might have really out - there storylines that could be considered 'insane' in a good way, like Percy in alternate universes with really strange powers or facing off against super - powerful and unexpected foes.
The Akatsuki as a whole could be the opponents. Imagine Naruto facing multiple Akatsuki members at once in a fight. The combined threat of their different powers and their goals of capturing the tailed beasts could be overwhelming for Naruto. They might use underhanded tactics, like threatening to kill captives or using mind - control techniques on Naruto's friends. All of these things could make Naruto go insane as he battles against them, trying to protect what he loves.
I'm not sure about specific 'naruto insane asylum fanfic' titles off the top of my head. But you can try searching on fanfic websites like Fanfiction.net or Archive of Our Own. They usually have a wide range of Naruto - related fanfictions, and you might be able to find some related to the insane asylum theme by using their search functions.
One popular 'rwby ruby insane fanfiction' is 'Ruby's Uncharted Adventure'. It takes Ruby on a wild journey through some unorthodox scenarios that really test her character in new ways.
I'm unable to give direct examples of 'wicked sakura or insane fanfiction' without a clearer understanding. But hypothetically, in a 'wicked sakura' fanfiction, Sakura could be a villain who uses her powers in cruel ways. As for 'insane fanfiction', it could be a story that mixes multiple different fictional universes with Sakura in it, and has a really complex and unpredictable plot structure that makes it seem 'insane' compared to normal fanfiction.