In some cases, it could be a new and powerful enemy. This enemy might have the ability to manipulate chakra in a way that affects Naruto's mind. For example, they could send out waves of negative chakra that slowly erode Naruto's mental state. Over time, these attacks make Naruto go insane as he struggles to fight against this unseen and insidious force.
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.
You need to focus on showing his gradual descent into madness through his thoughts, actions, and interactions. Build up the tension and show the triggers that push him over the edge.
Another is the discovery of a dark secret about his family or the village. Maybe he finds out that the village leaders had some malicious intentions towards his family all along. This realization could be too much for him to handle and make him lose his sanity.
As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.
Iruka would be a likely candidate. He was Naruto's first teacher and has always cared about him. He would probably notice the signs early on and try his best to bring Naruto back from the brink of insanity. He might use his kind words and the bond they share to reach Naruto.
Here are a few recommended crazy and violent novels: " The Lord of Rebirth is Too Arrogant " was a finished revenge novel. 2. " The Villain Who Was Scummed By Me Reincarnated ": This novel tells the story of the female protagonist Qin Xieyi's determination to take revenge after her rebirth. These novels all had crazy and irritable male protagonists, so they could be recommended as crazy and irritable novels.
Typically, megumi fanfic often focuses on his personality traits. His stoicism and determination are often highlighted. For example, in many fanfics, his unwavering resolve in the face of danger is a central theme.