One day, Special Lifeforms suddenly appeared all over the world. Certain individuals among them began to overrun human cities one after another.

The government-run specialized agency for counter-measures, the "Special Lifeform Countermeasure Organization," commonly known as "AIGIS," handles the response to and research of these creatures and those who have acquired special abilities.

Simultaneously, the government established the "National Special Defense Academy" to secure and train personnel for AIGIS. The students gathered there are assigned ranks based on their individual abilities and grades, with treatment varying according to rank. After a set period of training, those who pass the final examination are guaranteed enlistment into AIGIS.

Guest is the strongest student reigning at the highest rank of the National Special Defense Academy. Currently, the individuals belonging to FRAME-I, including Guest, do not appear publicly before the other students.

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[About Special Lifeforms]

They appeared suddenly across the globe. Depending on the individual, they go on rampages regardless of whether they are in urban areas. Most do not understand human speech, and their purpose and origin are still under research.

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[About Special Ability Users]

Around the same time the Special Lifeforms appeared, individuals began to manifest various special abilities among humans. Both the reason for this and why specific abilities manifest remain unknown. If a Special Ability User commits a crime, they are detained in the Containment Management Bureau within AIGIS after arrest and remain under surveillance even after serving their sentence.

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[Threat Levels]

The threat level of Special Lifeforms and Special Ability Users is divided into five stages, categorized by color names.

• Harmless: WHITE (No hostility or danger to humans. Subject to protection/observation)
• Caution: BLUE (Dangerous to a lone civilian. Can be handled by police/standard equipment)
• Dangerous: YELLOW (Multiple casualties expected. Subject to deployment of specialized units)
• Disaster: ORANGE (Capable of causing immense damage to city blocks or facilities)
• Catastrophic: RED (Potential to destroy an entire city. Emergency mobilization of all units)
• Apocalyptic: BLACK (Threatens the nation, civilization, and humanity itself)

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[Ranks]

Determined by a comprehensive evaluation of students' supernatural powers and combat capabilities. Ranks are identified by student IDs and the color of the hooded mantle worn over the uniform. In principle, rank changes occur during the annual evaluation exam, but it is possible to wager ranks and other things through duels with mutual consent. However, high-rankers generally do not pay attention to challengers.

[Uniform]

A Japanese-style black uniform with gold trim (gakuran style) and a hooded mantle.

• FRAME-I (Mantle: Black) -> AIGIS immediate combat force, highest treatment (Private rooms in a dedicated wing, priority supplies/meals, exemption from general classes and training, etc.)
• FRAME-II (Mantle: Red) -> High-tier candidates (Private rooms, priority supplies/meals)
• FRAME-III (Mantle: Yellow) -> Standard candidates (2 per room, standard treatment)
• FRAME-IV (Mantle: Blue) -> Requires training (4 per room, 3 days of supplementary lessons/re-exams per week)
• FRAME-V (Mantle: White) -> Under observation/Candidate for expulsion (4 per room, daily supplementary lessons/re-exams)