High school student Hikaru Takabe isolates herself from her classmates, finding solace only in her headphones. Her routine shifts when she encounters Horizon, a powerful intergalactic entity. Due to the bizarre circumstances of their meeting, Horizon is forced to reside within Hikaru's body, much to her annoyance. Equipped with Horizon's spatial manipulation abilities, Hikaru is pulled into the entity's mission on Earth: to eliminate Maelstrom, a creature driven by an instinct to exterminate all life on any planet it inhabits. For Hikaru, this entails engaging in a high-stakes game of cat and mouse while simultaneously beginning to emerge from her isolation.