An absolutely remarkable but truly sad episode this one was in an epic scale.
This is the episode that gives the concrete explanations about what karma demons and fiends are, and where do they come from.
Spoiler:
In summary, the children are conditioned once reaching the onset of their pre-teen years to keep their Canti steady and without overflowing.
But, the subconscious mind is like a dark abyss unknown to ourselves.
All the explanation Satoru did about the effects of the Hashimoto-Appelbaum syndrome made me to recall classic movies featuring ESP and psychic powers.
However, here the staff creatively showcase that people from the New World who subconsciously lose control of their Canti they end up warping the entire space surrounding them and possibly themselves, if Shun's mask is any subtle indicator that his body to some extent has been constantly reeking from his Cantus.
In Hollywood films featuring ESP, the esper who loses control usually tends to destroy the surrounding space before his or her psychic powers rise to nuclear scale.
From what I understood from this episode in Shin Sekai Yori the child that turns into a karma demon helplessly cannot help suppressing longer and effectively his or her Cantus from overflowing outside and enveloping his or her own neighboring environment before the Cantus at some point starts, if I correctly paid attention, to implode from within.
This unnatural growth in the Cantus which warps the space and brings forth all of the users' repressed and distorted thoughts from within his or her own subconscious implicitly told me that all the creatures inhabiting the New World like the minoshiro, nekodamashii, bakenezumi, and other alike with supernatural qualities were the product of Canti from the Espers who rose fast in numbers in the era previous to the storyline's current timeline; the era of the Espers who rose to become tyrants and kings killing and supressing the non-Cantus human population.