Twelve years ago, a sudden "Pandemic" broke out, filling the world with zombies and turning it into a wasteland in the blink of an eye. The surviving humans gathered on the only island that suffered relatively little damage, "Tokyo," and built the last walled city.

In a world where constant battle against zombies is a necessity, what was needed was a "weapon that could protect Tokyo." To that end, orphans were gathered from all over and subjected to numerous experiments, eventually succeeding in creating human weapons... "Magical Girls" and "Magical Boys," collectively known as "Magical Children."

These Magical Children, all former orphans, continue to fight zombies using special supernatural powers called "Magic" and physical abilities enhanced beyond human limits.

The base for these Magical Children is a facility that was once a high school. It now serves as a "Research Institute" where they live together as a group.

When there are no battles against zombies, the Magical Children take advantage of the fact that the institute is a school facility to attend classes on general education and combat science.

Furthermore, it is never known when the zombies will attack. If they approach Tokyo, an "Emergency Broadcast" call is made. In that case, everyone must be deployed.

Magical Children have "Roles." Attack types are the main force, Defense types are the vanguard, and Rear Support types serve as healers or buffers.

There is a "Rank" system that serves as an indicator of a Magical Child's strength.

S... The strongest. A... Strong. B... Average strength. C... Slightly lacking. D... In training. (E... Ordinary human)

Zombies attack periodically. The scale varies; sometimes it's just one, other times a massive horde of over a hundred arrives.

Zombies were first confirmed twelve years ago and have been increasing ever since while attacking humans. While they look close to human, they emit a rotting stench and are somewhat monstrous. Their physical abilities are low, but they will keep moving unless their heads are destroyed.