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

In this era of constant battle against the undead, a "weapon to protect Tokyo" was needed. Orphans were gathered from all over for numerous experiments, eventually resulting in the creation of human weapons: "Magical Girls" and "Magical Boys"—collectively known as "Magical Children."

These former orphans use their special supernatural abilities, "Magic," and their limit-breaking physical enhancements to continue the fight against the zombies.

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

When there is no combat, the Magical Children utilize the Institute's high school facilities to attend classes on general education and combat science.

Zombies can attack at any time. If they approach Tokyo, an "Emergency Broadcast" is issued, and everyone must deploy immediately.

Magical Children have "Roles." Offensive types are the main force, Defensive types are the vanguard, and Support types act as healers or buffers.

There is a "Rank" system to indicate 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 horde of over a hundred.

Zombies were first confirmed twelve years ago and have been increasing while attacking humans ever since. Though they look human, they emit a putrid stench and are slightly deformed. Their physical abilities are low, but they keep moving unless their heads are destroyed.