It all began with the first 'Gate' that appeared in the United States.

An unidentified dimensional rift emerged in the middle of a city, and from within, creatures humanity had never encountered—'Kaiju'—revealed themselves.

Kaiju from the early Gates were at a level that could be sufficiently suppressed with modern firearms and armored forces. Nations around the world recognized this as a new form of biological disaster and mobilized their militaries to control the situation.

However, that was only the beginning.

As time passed, the Gates grew larger, and the Kaiju became incomparably more powerful. With high intelligence, overwhelming physical abilities, and even special supernatural powers, these Kaiju could no longer be countered by conventional weaponry.

Around that time, another change appeared in humanity.

Due to the influence of the Gates and Kaiju, transcendental abilities began to naturally manifest in some humans. People started calling them 'Sentinels'.

However, naturally occurring Sentinels were extremely rare and, above all, were not under state control. How and where they used their abilities was a matter of individual choice. As the Kaiju threat spread globally, the need for a Sentinel force that the state could control became urgent.

Eventually, major nations established an international joint research system and pushed forward with a plan to develop humanity's first artificial Sentinels.

Artificial Ability Injection Project (AAIP)

This was a project to artificially awaken Sentinel abilities in human bodies using biological materials extracted from Kaiju and special energy secured from the Gates.

Most test subjects were soldiers and special forces members from various countries.

However, it was extremely rare for a human body to accept such power. Numerous subjects lost their lives to physical collapse, organ damage, mental instability, and power rampages, resulting in an extremely low success rate.

Nevertheless, the research did not stop.

After countless sacrifices, artificial Sentinels who could use their abilities stably finally began to be born.

이들은 자연 발생 센티넬과 달리 국가의 관리와 통제 아래 놓였으며, 괴수 토벌을 위한 전략 병력으로 운용되었다.

However, a new problem was discovered.

The more they used their powerful abilities, the more extreme the burden accumulated on the Sentinel's mind and nervous system. If left unattended, this led to sensory overload, mental instability, and eventually, uncontrollable rampages.

In that process, humanity discovered another type of being.

People with the ability to stabilize a Sentinel's mental and sensory burden and suppress their rampages.

They would later be called 'Guides'.

Once the existence of naturally occurring Guides was confirmed, research institutions in each country pushed for new plans to secure and manage them.

Guide Acquisition Project (GAP)

Since then, Sentinels and Guides have been managed as core strategic assets of the state.

If the Sentinel was the spear that faced the Kaiju, the Guide was the hand that held that spear so it wouldn't break.