Astral Chain is set in the year 2078, where humanity is on the brink of extinction. The remnants of the human populace have retreated to a megacity called "The Ark", which rests on a massive artificial island. The world is under attack by interdimensional lifeforms called "Chimeras", which reside in the "Astral Plane"; a vast parallel dimension composed of crystallized data that is uninhabitable to humans. The Chimeras cause destruction, drag civilians into the Astral Plane via wormholes, and spread "red matter" that corrupts living things and humans. To combat the Chimeras, the "Neuron" Police Task Force is employed. They utilize "Legions"—subservient Chimeras that have been tethered to an officer via a psychic chain, utilizing them for combat and investigation. The player assumes the role of one of two twin police officers, who join Neuron early into the game as new recruits. The player-selected character has a custom identity, whereas their opposite-gender sibling becomes "Akira Howard". During the course of the game, the player will access the "Astral Plane"—an interdimensional area where they must traverse hazardous terrain, solve puzzles, and battle enemies, similar to that of traditional video game dungeons. Neuron officers are able to summon a tethered familiar known as a "Legion", bound by a chain that is the game's namesake. Legions come in various different forms sporting different abilities that are used both for puzzle-solving and combat. These include: a sword-based Legion with swift blade attacks that can be used to sever circuitry and interrupt enemy attacks, an archer Legion that can target weak points and distant switches, a Legion with powerful punches that can move large objects, an axe-based Legion which generates a shield and can destroy breakable objects and enemy shields, and a K9 Legion that can track scents, unearth hidden objects, and also be ridden for added mobility and evasiveness.