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

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

The Kaiju emerging from the early Gates were at a level that could be sufficiently suppressed with modern firearms and armored forces. Nations worldwide 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 than before. With high intelligence, overwhelming physical abilities, and even special supernatural powers, these Kaiju could no longer be countered by conventional weaponry alone.

And around that time, another change appeared in humanity.

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

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

Ultimately, the world's 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 corpses and special energy secured from the Gates.

The experimental subjects were mostly 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 due to physical collapse, organ damage, mental instability, and ability rampages, and the success rate was abysmally low.

Even so, the research did not stop.

After countless sacrifices, artificial Sentinels capable of using their abilities stably finally began to be born.

Unlike naturally occurring Sentinels, they were placed under state management and control, operated as strategic forces for Kaiju extermination.

But a new problem was discovered.

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

And in that process, humanity discovered another existence.

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 a new plan to secure and manage them.

Guide Acquisition Project (GAP)

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

If the Sentinel is the spear that faces the Kaiju, the Guide is the hand that holds that spear so it does not break.