"If we erase a Palace, there's no doubt that the persona's distorted desires will be erased as well. But desires are what we need in order to survive. The will to sleep, eat, fall in love- those sorts of things... If all of those yearnings were to vanish, they'd be no different than someone who has shut down entirely. They may even die if they're not given proper care."
A mental shutdown is a major plot element in Persona 5.
- Persona 5 / Royal
A mental shutdown occurs a unspecified amount of time after a person's Shadow Self is destroyed in the Metaverse. The reason for this a Shadow Self is made up of the orginal persona's desires, including the desires for normal functions in life, such as to eating, sleeping, and emotional things such as love. Therefore, a destroyed Shadow will cause a mental shutdown after a period of time, although the symptoms beforehand can be similar to a successful Change of Heart. It is the more extreme form of a Psychotic breakdown.
A mental shutdown causes one to undergo symptoms of similar to a sudden heart attack, their eyes rolling up to the point of their pupils being obscured as they drool a black liquid, as well as little sense of what's going on around them. Usually, mental shutdowns have a high chance to end with death.
Two years before the events of Persona 5, the first Metaverse-related incidents begin to arise, starting from Goro Akechi being given a Persona and the Wild Card ability by the master of Mementos, who used him to instigate chaos among the public.
After learning about Wakaba Isshiki's research, a conspiracy led by Masayoshi Shido learned of her research on cognitive psience. Teaching his illegitimate son Goro Akechi about the Metaverse, he triggers a mental shutdown in Wakaba, causing her to fall in front of a car. He then covered up the incident as Wakaba committing suicide due to regretting birthing Futaba, causing her to be torn by suicidal depression to the point that she closed herself in Sojiro's room so hard that nobody in Yongen-Jaya knew about her, and repressing the memories of the symptoms Wakaba had when undergoing the mental shutdown until they were recalled upon viewing Kunikazu Okumura's mental shutdown. Futaba knew nothing of Shido's role behind it before Okumura's death and meeting the IT Company President's (Fake Medjed) Shadow Self in Shido's Palace.
After this, Akechi started a string of Mental Shutdowns for Shido's political gains, such as killing anyone Shido deems incompetent and "solve" the cases himself, although he's known to be hired by Shido's political opposition (such as Okumura) as well. In reality, Akechi is disloyal, and he only started the killing spree to make sure Shido inaugurates so he can expose his crimes to shame him (considering implications that Akechi was born when Shido had a one night stand with a call-girl, this will most likely be fatal to his career), an act which would most likely cause nationwide discord and chaos. Supposedly, he will then create society anew.
While it did not happen, Morgana warns the protagonist, Ryuji Sakamoto, and later Ann Takamaki about the possibility of causing a mental shutdown when discussing the idea of removing Suguru Kamoshida's Treasure and "distorted desires", as he never had caused a Change of Heart before. Later, after Junya Kaneshiro's Shadow mentioning someone in a black mask using Palace for their own gain, including triggering mental shutdowns, the Phantom Thieves of Hearts take heed of his warnings.
However, due to having their major financal pillars uprooted by the Phantom Thieves, Masyoshi Shido's conspiracy begins to target them. The plan to end the Phantom Thieves started with a fake medjed threat to induce a false popularity increase on the Phantom Aficionado Website via a grossly inflated view counter, then prod the Phantom Thieves into a heist against Kunikazu Okumura, an overly ambitious CEO who was attempting to compete with Shido for presidency. It was revealed that Okumura used the Black Mask's services to induce mental shutdowns against his disloyal board members and competition outside of his company, all of them who supposedly suffered from mental illnesses. The conspiracy aims to trigger multiple mental shutdowns to frame the Phantom Thieves for Akechi's past and future actions, to reduce their popularity, and to kill Okumura, who would have revealed the person behind the mental shutdowns if he had a change of heart. The decision also partially stems from that Okumura was the only candidate for prime minister capable of acting as an obstacle to Masayoshi Shido.
In advance, Principal Kobayakawa (because of his failure to figure out which students caused Kamoshida's change in heart at Shujin Academy, his predicted attempt to ask the police for help, and the implication that the party was the reason why he was principal in the first place) was subjected to a Mental Shutdown leaving the police building and ran over by a oncoming truck in his disabled state, with a fake Calling Card planted in his office to frame the Phantom Thieves. When Okumura was defeated in the heist, Akechi in his "black mask" outfit triggers a fatal mental shutdown in him by killing his Shadow Self directly after the Phantom Thieves stole his Treasure, killing him exactly before he could expose the leader of the Conspiracy. It was also implied that there are plans of eventually triggering another mental shutdown in prosecutor Sae Niijima, who was pursuing the case as well and had obvious second thoughts about her bosses, as she noticed the possibility of a group separate from the Phantom Thieves.
After the police raid on the Phantom Thieves in Sae Niijima's Palace, should the protagonist successfully survive the interrogation and return to the present, the conspiracy falsely assumes that he was killed by Goro Akechi. Having been confident that the Phantom Thieves case is solved for good, the Conspiracy betrays the SIU Director and he was subjected to a mental shutdown as well.
After Akechi was defeated in Shido's Palace, and subjected to an ambiguous end, Shido's change of heart and subsequent confession, and the defeat of Yaldabaoth that removed the Metaverse Navigator and so access to the Metaverse, it became impossible to commit mental shutdowns.