Oh boy, I was made for this thread.
Real life NHK
Welcome To The NHK is a book that got adapted into a manga and anime. It revolves around a hikikomori named Satou who, during a trip on psychedelic drugs, invents a conspiracy theory about a secret organisation called the Nihon Hikikomori Kyokai whose goal is to turn people into hikikomori. How wacky, right? However I believe that this exists in real life. First of all, why? Every society needs someone to look down on. If you have seen Assassination Classroom you will see what I mean: they use the people in the lowest class and treat them like scum in order to encourage others to succeed and not end up like the bottom of the barrel losers. It is the same thing in real life. Time and time again the bottom of the barrel in society and demonised. For example the otaku panic following the Tsutomu Miyazaki murders or the incel panic now. Canada has banned incels as a terrorist group despite the fact that they are neither terrorist nor a coherent group. Look at how often people use incel as an insult and make such a big deal out of incels. But how many incel attacks have there been? Barely any, especially compared to any other ideology (and I am hesitant to call incel even an ideology). Hikikomori are getting a similar treatment without people really saying it. I keep hearing about the dangers of internet radicalisation and how people are shutting themselves in their rooms and getting recruited into extremist groups online. Can you actually think of any cases of this though? Where a shut in was radicalised and became a terrorist? Internet radicalisation is a big problem but it is not shut-ins. These people are usually out in the community and that is usually where it starts.
As for how exactly this becomes them creating hikikomori, look at their treatment of undesirables. Incels are practically the laughingstock of the world and the news and governments demonises them, while the mentally ill are constantly shunned and cast out from society. I have experienced this personally as when I was at school the school itself victimised me by not caring about my problems. I would sit and cry in a completely silent room and no one, student or staff, would care. They made my mental health worse and then told me if I did not get my act together I would have to leave school so I did leave. Schools obviously answer to the government. Bullying of the mentally ill is rampant in schools to the point where school refusal is common. Even when these people are driven to murder the riajuu mock the mentally ill further by calling them school shooters. Talk about a self fulfilling prophecy. Schools, under the direction of the government, ignore bullying of those that are at risk of mental illness or are just considered undesirable in order to push them into becoming hikikomori. They also feed propaganda to hikikomori to make them less hopeless to try and get them to participate in society in order to cause further harm, cementing the hikikomori's place in their mind and showing them that they cannot participate in society and must accept their fate.
TLDR: the government ostracises and demonises undesirable people to cause them to become recluses in order to create groups of people for wider society to look down on in order to boost morale
The government is using microwaves to control people's thoughts.
Based off the Havana syndrome where the government suggested it was caused by a microwave weapon which shows that such a thing is feasible, and the amount of people who believe in messages being sent to them via electromagnetic waves. In Japan, they even have the word "denpa" to specifically describe people who believe such a thing. That is something very specific, you would think if it is just a psychotic delusion that people's stories would all be different but it is the same cause: electromagnetic waves. And some even get more specific and blame microwaves. I did not even know what electromagnetic waves were until I heard of this. I constantly experience intrusive thoughts and as soon as I heard about this is made sense but it was rejected by my mind. It was like something was trying to suppress it. Such a thing has never happened before nor since.
It has no obvious cause either. For example, thought based delusions can be chalked down to the disorganised thinking symptom of schizophrenia or natural human fears becoming delusions. However the electromagnetic wave aspect is oddly specific. Too oddly specific. I have a feeling that 5G and 6G may be being used to upgrade this as well, but that is probably a stretch on my part.
Those are my main ones, I have more, mostly original (imagine The Protocols Of Elders of Zion but run by feminists instead of Jews) and some that I have taken up (I am a firm believer of the dead internet theory mainly because people online often tend towards the extremes in everything and that seems very unnatural to me) but I might write those later.
I will end this by mentioning that I have not been diagnosed with schizophrenia nor any psychotic disorder as of the time of me writing this.