High school student Luna Amano struggles to remember the past five years of her life. Her older sister, who had promised to help her create new memories, has vanished without a trace. Alone and clinging to fragmented recollections, Luna dedicates herself to running the flower shop her sister left behind, holding onto the hope that she will one day return.

Luna’s quiet routine is shattered when a group of yakuza working for her landlord begins pressuring her to sell the property. When she refuses, the thugs burn the flower shop to the ground in an attempt to eliminate her. In the ensuing confrontation, Luna’s instincts take over. She grabs a dropped gun and, with deadly precision, kills her attackers. As the violence erupts, hazy memories flood her mind, awakening lethal combat skills she never knew she possessed.

Now driven by a fierce desire for revenge, Luna embarks on a bloody quest against the men who destroyed her sister’s legacy. She soon discovers that she may be connected to a sprawling criminal organization known as the Round Table, which controls crime across Japan. The narrative strongly suggests that Luna is a sleeper agent, part of a rumored experiment involving former Soviet scientists who brainwashed individuals to become assassins known as the Knights of the Round Table.

The story follows Luna as she fights through the criminal underworld, seeking answers about her forgotten past and the source of her deadly precision. She wants to understand why she is so capable with a gun and what happened to her sister.

The manga concluded its serialization with three compiled volumes.