In a world governed by the law of "heroic spirits summoning", humans use mysterious rituals to summon heroes from history and legend as "heroic spirits" to fight against the disaster that threatens the world - the "dark abyss". The Dark Abyss is a chaotic force that consumes reality, awakening every few hundred years and trying to drag the world into endless nothingness. In order to fight against the Dark Abyss, various countries and organizations formed "Summoners' Guilds" to summon heroic spirits to fight through contracts.
