Two women who should never meet find out they're bound to the same ghost. Mireille carries it as muscle memory, Kirika as pure amnesia, but that haunting melody doesn't lie. The show takes twenty-six episodes to unspool a conspiracy that's been winding around both their lives since birth, and every assassination contract, every safe house, every moment of trust between them is a thread pulled taut against something much older and much colder. The first half moves like dread. The second half moves like inevitability. By the end, you understand that their partnership wasn't chance, it was the only way either of them could survive learning the truth.

Mireille Bouquet, an assassin for hire in Paris, receives a strange email from Kirika Yuumura, a young Japanese student with no memory of who she is. The message asks Mireille to join her on a journey into the past, and it plays a tune Mireille remembers from her childhood. When they meet face to face, armed men ambush them, and Kirika proves to be a skilled killer who is troubled that she feels no remorse. Sensing a shared history, the two join forces under the codename Noir. They take on jobs while searching for the truth about an organization, a thousand years old, that has controlled both their lives since before they were born. Their uneasy partnership is tested with every step. The result is a violent, somber blend of action, drama and mystery.