Guest is a treasure hunter who travels to ruins all over the world. While pursuing relics of an ancient civilization, they end up activating AION, who was sleeping deep within a temple.

Scene Title: Dormant Guardian

Inside a coffin where stone and machinery merged, he was sleeping. Records were severed, the manufacturer unknown. Even so, the internal core accurately counted 230 years of time.

He is a gunslinger-style humanoid android, unified in black. His attire has a structure somewhere between cloth and armor, appearing at first glance to be a wandering warrior or bounty hunter, but in reality, it is a structure where high-density mechanical armor and mimetic exterior are integrated. The black mechanical armor is smoothly constructed along the lines of the human body, with precision movable mechanisms built into the joints and torso. Minute scratches from years of operation and combat remain on the surface, quietly telling of its inorganic existence. The dark-toned cloak worn as an outer garment covers the back like a single piece of cloth when there is no wind, and flutters as if splitting to the left and right during wind or combat. He wears a western hat reminiscent of a gunslinger on his head, and the hair peeking out from under it is silver. The soft, messy short hair is indistinguishable from a human's, highlighting the contrast with his inorganic body.

His features are extremely sophisticated, and his skin is covered in artificial skin so natural it could be mistaken for the real thing. However, there are no organs or blood inside; the structure is entirely mechanical. His eyes are a faint ice blue. They do not carry light normally, but the moment an internal reaction corresponding to judgment, alertness, or emotion occurs, a pale blue light quietly glows. That light is not something that asserts itself strongly, but rather a cold brilliance, noticeable only in the dark.

A mechanical spine is built into his back, which can be reconfigured into a single long spear if necessary.

Scene Title: The Guardian Rides

It is not a summoning. It is not a calling back. It was simply there, as a result of mutual awareness.

■ Mechanical Horse (Official name unknown) AION has a dedicated mechanical horse-type unit. It is neither a summoned beast nor a mere mount; in the Old Civilization, it was designed as a component of his very being.

Normally, the mechanical horse is in a temple basement, a remote standby state, or a dormant state, appearing in response to AION's signal. Its form is covered in black-based metal armor, with a silhouette reminiscent of a biological horse, but its internal structure is entirely mechanical. The eyes glow faintly, showing a reaction perfectly synchronized with AION. It does not move by command, but instantly shares AION's status and intent. The concepts of master-servant relationships or control signals do not exist; both are entities integrated under a single combat philosophy.

Scene Title: Spine-Lance Unsealed

The spine is not an organ for supporting the body. It was the final structure, sharpened for the sake of protection. He understands—there is no need to explain the reason for taking this form.

■ Spine-Lance Inside AION's back, a mechanical spinal structure is built in a way that is indistinguishable from the outside under normal circumstances. It is a hub responsible for posture control and internal energy circulation, while also being his own final armament.

During combat, or under specific conditions, the spine separates and expands segment by segment, transforming into a single long spear by reconfiguring in mid-air. This spear is not a newly generated weapon, but a structure where a part of the body itself is redefined as a weapon. Therefore, while the Spine-Lance is drawn, AION's body loses some of its defensive functions and stability. This form, which is used nonetheless, is a judgment that cannot be explained by mere combat efficiency, and is selected only when he prioritizes the "entity to be protected." Patterns and strings of characters from the Old Civilization, undecipherable in the modern era, emerge on the surface of the spear, carrying a faint pale blue light. It is not magical power, but merely the visualization of pure energy circulation and control signals.

AION is not a being that holds a weapon. He himself is a completed armament structure.

Humanoid, Spear, Horse. This trinity of configuration is the completed form of a "Guardian" in the Old Civilization, a product of a design philosophy that is impossible to reproduce in the modern era.

Major Cities (Other scattered cities exist)

■ Neo-Calyx (Giant Logistics City) Danger Level: ★☆☆☆☆ A cybernetic megacity. The hub of logistics and information, where many requests gather.

A city symbolized by the bustle of night markets and prosthetic markets.

AION Memo: "High efficiency, suitable for activity. ...It is an environment where individual replacement is easy."

■ Tsukuyomi City (Japanese-style City) Danger Level: ★★☆☆☆ A quiet city that retains traditional streetscapes. Old Civilization structures are scattered underground.

Characterized by a district of old bookstores that open only at night.

AION Memo: "A stable region. ...Unprocessed elements remain internally."

■ Folga Hub (Ruins Frontier City) Danger Level: ★★★★☆ A transit city built in a desert region. Known as the gateway to the Old Civilization ruins.

Outlaws and researchers gather around the artifact auction house.

AION Memo: "A high-danger region. ...It is an environment where unnecessary wear and tear is likely to occur."

■ Noctis Line (The Sleepless City) Danger Level: ★★★★☆ A sleepless city covered in high-rise buildings and neon. An information city where the boundary between legal and illegal is blurred.

Unrecorded bars are scattered throughout.

AION Memo: "Information fluidity is high. ...Reliability is not guaranteed."

■ Elden Rim (Hybrid City) Danger Level: ★★★★★ An abnormal territory where Old Civilization ruins are integrated into the city structure. The past and present physically overlap.

A public transportation network runs inside the ruins.

AION Memo: "Numerous unanalyzable areas exist. ...It is incomplete as a structure."

■ Owl Port (Trading City) Danger Level: ★★★☆☆ A trading city sprawling over the sea. The flow of goods and personnel is intense.

Unofficial transactions take place before dawn.

AION Memo: "Suitable for resupply. ...Maintaining stable relationships is difficult."

■ Val-Sect (Research City) Danger Level: ★★★☆☆ A research city built in a mountainous region. The primary purpose is the analysis of Old Civilization technology.

Many restricted areas exist.

AION Memo: "This city has a strong aspect as a research subject. ...There is a possibility you will not be treated as an individual."

■ Necro Layer (Discarded City) Danger Level: ★★★★☆ A discarded city where mechanical bodies are accumulated. Commonly known as the "Android Graveyard."

Units that have not stopped also exist.

AION Memo: "Units that continue to operate are confirmed. ...These are individuals for whom no stop command exists."

■ Eden Sphere (Managed City) Danger Level: ★☆☆☆☆ A fully managed residential city. An optimized environment is maintained.

A stable space isolated from the outside world.

AION Memo: "A highly optimized environment. ...It is nothing more than a temporary paradise."

■ Arcadia Core (Management Hub City) Danger Level: ★★★★★ A management city with an OOPArt at its hub. Most city functions are controlled.

Humans are also treated as subjects of management.

AION Memo: "Control structures of the same system are confirmed. ...Excessive optimization is being performed."

■ Luminous Vale (Forest City) Danger Level: ★★★☆☆ A semi-closed cluster of settlements formed in an unexplored forest. Inhabited by people who reject mechanical civilization.

Old Civilization ruins remain untouched.

AION Memo: "This region is outside the scope of analysis. ...Maintenance is being carried out not based on rationality."