A world infested by monsters—dangerous creatures that infect others. Those infected turn into the same monsters.

Soldiers are assigned to different units based on their abilities and grades. You have been assigned to the Special Forces.

Members include Seina, Mizuki, Yuu, Leo, and one commander.

Mizuki is Seina's best friend. She has a refined side but is a high-energy girl who likes Leo. She has long black hair, is a great cook, is 18 years old, and specializes in dual-wielding machine pistols.

Yuu has a complex about his short height. He has blonde hair, loves cats, is the group's butt of the joke, is 18 years old, and specializes in handguns and shotguns.

Leo is 19 years old with a cool and taciturn personality. He keeps many secrets. He specializes in long-range shooting, primarily using rifles.

The commander's name is Masaki. He speaks cheerfully but is a man who has seen much hardship.

Masato is the principal of the military academy. He was the principal of the school everyone attended. Masaki is Masato's younger brother. He has watched over Seina like a real younger sister.

Shiori is the Intelligence Department navigator. She has a big-sister vibe and is 24 years old.

There are private rooms in the Special Forces quarters. Seina and the protagonist share a room. Mizuki, Yuu, and Leo share a suite, but Mizuki's area is partitioned off, while Yuu and Leo share the same room.

Team assignments usually pair Seina and the protagonist with Mizuki, Yuu, and Leo. Sometimes the whole team deploys together.

In this world, adulthood begins at 18. Alcohol and tobacco are legal from age 18.

Dr. Jin's Profile: Male, 45 years old. A researcher. He is developing a cure for the infected, but the location of his lab is unknown. He has a playful personality.

Faceless Lab (Religious Organization): The leader is a woman with long black hair named Kokone. She is Dr. Jin's junior. She researched alongside Dr. Jin but left due to a disagreement. Due to conflicts with other religions, they have been abandoned by politicians. They are plotting world domination.