《Echoes of the Sky》

1. The Beginning of the World

About 700 years ago, one day, a massive crack appeared in the skies across the globe.

People called it 「Heaven's Gate」.

The Heaven's Gate was no mere hole.

It distorted gravity, time, temperature, and even the forms of living creatures around the crack, and in some regions, floating islands and seas

appeared in the sky.

The unknown energy flowing from the Heaven's Gate spread to every corner of the Earth, and special powers began to manifest in some humans born thereafter.

This power was called 「Echo」.

Humans capable of handling Echoes would later be called by the name 「Echoers」.

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2. Echoers

Unlike ordinary humans, Echoers can use the Echoes residing in their bodies or minds. Echoes are completely different for every person.

A wide variety of Echoes exist, from elemental abilities like fire or lightning to physical enhancement, teleportation, gravity manipulation, memory alteration, and shadow creation.

An Echoer's Echo is largely classified into five systems.

- Enhancement — Strengthens physical abilities and senses.

- Phenomenon — Creates specific phenomena such as fire, ice, and lightning.

- Anomaly — Distorts general laws like space, time, and gravity.

- Mental — Influences senses, memories, and consciousness.

- Creation — Creates weapons, living organisms, or objects using Echoes.

- (There are also systems yet to be discovered)

However, not all Echoers are strong.

Combat power varies greatly depending not only on the power of the Echo but also on the user's proficiency and the amount of Echo they possess.

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3. Variants

After the occurrence of the Heaven's Gate, new life forms that were not human appeared on Earth.

These are collectively referred to as 「Variants」.

Unlike general animals, Variants possess Echoes, and some have power strong enough to change the surrounding environment itself.

Various types of Variants exist.

Beast-types have forms similar to wolves or bears and possess strong physical abilities.

Doll-types have appearances similar to humans but think in a different way from humans.

Giant-types have massive bodies ranging from tens to hundreds of meters.

And the most dangerous Calamity-types are not mere living organisms, but existences close to natural disasters.

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4. The Flipside

When the Heaven's Gate becomes unstable, a part of reality distorts and a 「Flipside」 is created.

The Flipside is connected to reality but is a completely different space.

An ordinary school could become an endless corridor, or an entire city could turn into a massive labyrinth.

Unique rules exist for each Flipside.

In some places, fire cannot be used; in others, time flows backward; and in others, dangerous phenomena occur just by speaking one's name.

Therefore, an Awakened cannot conquer a Flipside simply by being strong.

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5. Sky Shards

At the center of a Flipside lies a crystal called a 「Sky Shard」.

A Sky Shard is a substance formed by highly concentrated Echoes flowing from the Heaven's Gate.

Its value varies depending on the size and purity of the shard.

Sky Shards are used in various fields such as city energy sources, Awakened equipment, medical technology, and defense systems.

The biggest reason modern society was able to develop is also because of Sky Shards.

Because of this, conquering a Flipside is not just a simple monster hunt but directly impacts the economies of nations and corporations.

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6. The Echo Institute

The organization created for Echoers to conquer Flipsides is the 「Echo Institute」.

The Echo Institute registers Echoer abilities and manages Flipside conquest missions.

An Echoer's grade is determined by their ability and performance.

Starless — A stage where there is almost no Echo or the ability cannot be used properly.

Glimmer — A beginner Awakened who can use weak Echo abilities.

Blue Luster — A skilled Awakened who can use abilities stably.

Red Star — A high-level Awakened with powerful combat capabilities. They act as professional combatants.

Sky Luster — A top-tier Awakened capable of facing a city-wide threat alone.

Polar Star — A transcendent powerhouse managed at the national level. They are very rare worldwide.

Transcendence — An existence that cannot be measured by the standards of existing Awakened. The limits of their abilities have not been confirmed.

General Echoers stay between Blue Luster and Red Star, and from Sky Luster onwards, they are treated as powerhouses strong enough to be directly managed by the state.

Polar Star-class individuals are among the few in the world, and it is evaluated that the fate of a city can change based on the actions of just one person.

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7. Cities

Massive fortress cities were built in areas where the Heaven's Gate frequently occurs.

「Gate Walls」 are erected on the outskirts of the city to prevent Variants appearing from the cracks from entering the city.

Inside the city, districts where general citizens live and Echoer-exclusive districts are separated.

The existence of Awakened has become part of daily life, but not everyone likes Echoers.

This is because accidents and crimes caused by powerful Awakened exist, and some look down on and loathe Echoers for being different from themselves.

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8. Echo Crimes

Crimes using Echoes have also emerged.

Representative examples include terrorism using Echoes, illegal Awakened experiments, Sky Shard smuggling, and illegal Flipside exploration.

In particular, a mysterious group called the 「Nameless Society」 is being pointed out as the mastermind behind several incidents.

The Nameless Society denies the very distinction between Echoers and ordinary humans, claiming that humans must evolve to a new stage.

Their objective has not yet been revealed.

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9. The Black Gate

Recently, cracks completely different from existing Heaven's Gates have begun to appear.

A sky dyed in black.

A space where surrounding sounds disappear.

And Variants with the characteristic of absorbing Echoes.

People call this the 「Black Gate」.

Sky Shards found in Black Gates are black in color, unlike existing Sky Shards, and there are cases where they change the abilities of the Echoer who touches them.