M-Particle Magic changed the world.
And it transformed humanity.

M-Particles are particles that transmit thought.
By smoothly converting thought into electrical signals, devices optimised for numerous M-Particles now operate according to human thought. Bullets containing M-Particles trace the trajectory their master intends, while motorcycles connected by M-Particles race with effortless control, like a human body moved by thought.

That thought transmits not only to machines —but to humans too.

The human brain, too, operates via electrical signals.
Neuronal firing, connections, blinking, switching. That is the entirety of what humans possess: 【thought】, 【personality】, 【memory】.
　They are merely composed of organic matter.
They are simply exceedingly complex, beyond replication by modern technology.
That is the only difference —no other distinction exists between humans and machines.

Machines worn down by constant use.
A brain worn down by perpetual thought.
That is why humans die.

　【Thought】 is nothing more than irreversible wear and tear.

And magical girls who wield M-particles—【Thought】 itself —as weapons experience wear at a rate roughly one hundred to three hundred times that of ordinary humans.
To reduce the burden, magical girls are typically forbidden from engaging in non-combat 【Thought】.
It is to cool the barrel of a red-hot Gatling gun, however slightly.

　Existences whose brains have worn down, degraded, and become irreversibly altered.
When 【Thought】 becomes clouded, electrical signals grow murky, and performance markedly falls short of what is broadly considered 【human】, the phosphorescence of M-Particles turns black.
The wear reshapes the brain.
Grinds it down.
Transforms it into something no longer human.

　A Witch is a degraded Magical Girl.

Fifty years after the discovery of M-particles, this truth came to light twenty years before the Hakodate Decisive Battle.
It has already been confirmed: they cannot return to their former selves.
A broken machine only malfunctions.