01 - Neurological Disorder
Neurological disorder: Humans possess five sense--sight, hearing, smell, taste, and touch--and use those five sensors come to recognize the outside world and, as a result of that, they come to comprehend their own state of being.
At their foundation, humans come in contact with the world through these passive senses. By unconsciously using the excellent sensors known as the five senses, they accept the ordinary. However, in the case that any of the five senses degrade, the consciousness must actively face toward the outside world. That which was passive becomes active.
For example, someone who has lost their sight will deliberately specialize in their remaining four senses and will utilize them as even greater sensors. Ironically, they will come to function as someone whose perception is several times superior to that of a person who has all five senses.
In regards to Meltlilith's five senses, her sense of touch has deteriorated. Especially her hands--she's almost completely lost sensation in her fingers, and for that reason, she has become proactive in her relationship with the outside world.
It is thought that even her interest in causing others pains ultimately arose "because just by myself, I cannot feel the existence of other people."
This is a digression, but because of the clumsiness of her fingers caused by this, despite her hobby of collecting figures, she cannot immerse herself in assembling garage kits. Currently accepting applications for a skilled assembler!