Some lights are not meant to be held.

In Elysium, one of Earth's largest cities at the end of the 21st century, Shiro, a legendary contract assassin, is hired by a mysterious organization to eliminate Vespera, an underground city figure with a background as a frontier pilot. Just before pulling the trigger, Shiro changes her mind.

Fascinated by Vespera, Shiro follows her to the Abyss, a nightclub in the upper city, where a masquerade is taking place. Unbeknownst to Shiro, Vespera is there to meet Professor Sparks and help her escape. Vespera mistakes Shiro for Sparks, and Shiro ends up helping her find the professor, who is being pursued by Kaylen, an independent mercenary hired to capture her. Before leaving the party, Vespera swaps Shiro's dagger for her fake eyepatch, leaving behind a message: “You know where to find me.”

With Vespera's help, Professor Sparks escapes and completes her research, developing humanity's first intergalactic Gate. Among the candidates for humanity's first intergalactic mission, Vespera is the only frontier pilot willing and able to take the risk. She becomes the first human to travel beyond the galaxy and return, activating an ancient Gate in the process.

Following the successful activation of the Gate, humanity begins exploring nearby worlds. Vespera chooses Shiro as her copilot. After becoming stranded on an alien planet, the two finally acknowledge their feelings for each other. Rescued and reunited with the expedition, they continue exploring new worlds and grow increasingly close.

Humanity begins colonizing habitable planets and activating dormant Gates across the galaxy. On one of these worlds, they encounter a sentient species resembling humans, with rabbit-like ears and the ability to share memories through physical contact.

During a ball in Elysium, Shiro and Vespera share what will be their last peaceful moment. A message interrupts the evening: a new colony has stopped answering. When they arrive on the planet, they only find one apparent survivor from the rabbit-eared people…

When the first Gate is activated on Earth, a wave of energy sweeps over the people nearest to it. Fewer than a hundred are touched, and almost all of them die. A handful survive, their bodies changed in ways no one can explain.

Years before the main story, in the shadows of Elysium, a young Shiro builds a reputation as a contract killer who only targets the worst criminals. Street whispers give her a name that will follow her everywhere: the White Ghost.

Shiro and Vespera are separated: Shiro is sent to defend Colony Alpha, Vespera to Colony Delta. Under constant Circle attacks, Shiro is not expected to win, only to hold. A powerful strike from PHOBOS, an experimental weapon with a technology derived from the Gates, annihilates the invaders on the ground while new Circle vessels keep on arriving on the colony.

The raids have taken Colony Delta’s garrison, and Vespera, the senior serving officer on the ground, assumes command of its defence. When a new assault comes, she draws it away from the colony by serving as bait with her own ship.

A Frontier pilot disappears into Omega, a remote zone of the Delta system, pursued by hostile units, while Earth’s command stays silent. Called by a legendary mercenary, Shiro leaves her post to join her on a mission into the heart of the enemy fleet and recover the missing pilot.