When Makoto Yuki is recruited to S.E.E.S. in April, Shuji Ikutsuki and Mitsuru Kirijo explain their understanding of Shadows and Apathy Syndrome to him. Shadows are beings that appear during the Dark Hour. In the event a normal person not transmogrified into a coffin during the Dark Hour, then they are likely to be attacked by a Shadow. The Shadows eat the minds of their victims, resulting in the victim becoming unable to speak or move. This condition is known as Apathy Syndrome, and those who have contracted it are called The Lost. If left to their own devices, they will perish due to malnutrition or accidents. Thus, one of S.E.E.S.' goals is to defeat Shadows and prevent more ordinary people from becoming The Lost.
It is later revealed that Ikutsuki was manipulating S.E.E.S. into defeating the Shadows that appeared during Full Moon operations so that they would recombine into Death.
During Chapter 3-19 of Story Mode, Naoto Shirogane says the true cause of Apathy Syndrome was when a Shadow left its owners body. Naoto believes the coma victims in Dancing All Night are similar to the victims of Apathy Syndrome. Except this time around, the Shadows are being forcibly removed from their owners, and the Shadows that they see on the Midnight Stage belong to the coma victims. Furthermore, the Investigation Team being able to wield their Shadows as Personas has prevented them from falling into the Apathy Syndrome-like coma.
In the Persona 3 lore and setting book, Persona Club P3, it is clarified that Shadows do not actually eat humans. The real cause of Apathy Syndrome is when a human loses the will to live and their Shadow leaves them. Shadows originated from Nyx but now exist as part of human minds, and being without their Shadow makes humans non-functional thus giving the appearance of what is called Apathy Syndrome. Defeating Shadows causes them to return to their respective humans and cures them of Apathy Syndrome.[1]
Despite the name, Apathy Syndrome is more akin to akinetic mutism than it is to apathy, mainly that akinetic mutism is the tendency to not move or speak due to diminished motivation while apathy tends to only hinder emotional stimulation and decrease productivity.
Nomenclature
Apathy SyndromeLost
Names in Other Languages
Language
Name
Meaning
English
Apathy Syndrome
Japanese
無気力症Mukiryoku-shō
Lack-of-Energy/Drive Disease
Simplified Chinese
无气力症Wú Qìlì Zhèng
Lack-of-Energy/Drive Disease
Traditional Chinese
喪失精力症Sàngshī Jīnglì Zhèng
Energy/Drive-Loss Disease
French
Syndrome apathique
Apathetic Syndrome
German
Apathie-Syndrom
Apathy Syndrome
Italian
Sindrome apatica
Apathetic Syndrome
Korean
무기력증無氣力症Mugiryeokjeung
Lack-of-Energy/Drive Disease
Polish
Apatia
Apathy
Brazilian Portuguese
Síndrome da Apatia
Apathy Syndrome
Russian
Синдром апатииSindrom apatii
Apathy Syndrome
Peninsular Spanish
Apatía
Apathy
Turkish
Apati Sendromu
Apathy Syndrome
The Lost may also be more formally called 無気力症患者Mukiryokushō kanja ("Apathy Syndrome sufferers") in Japanese.