By 2119, the vessel Green Sleeves discovered that three planets had been assaulted by X23, a sentient planet on a collision course with Earth. When the Earth government commanded the Green Sleeves to strike X23, its captain, Dr. Sugita, declined, arguing that peaceful coexistence was possible. Shortly after, contact with the ship was severed. Two years later in 2121, Susumu, Dr. Sugita’s son, is approached by mysterious individuals who escort him to Dr. Miya, one of the rare supporters of his father’s stance, as most of society viewed Dr. Sugita as a traitor. Dr. Miya urges Susumu to enlist in White Pegasus, a specialized medical rescue unit equipped with a Micronizer System that shrinks humans to treat illnesses from within. When X23 finally comes into visual range, the alien inhabitants known as Hues select Susumu’s friend as their initial target. Susumu and his White Pegasus comrades succeed in defeating the Hues inside his friend’s body, only for Susumu to discover that the signals emitted by the chips within the Hues are actually music composed by himself and his mother, intended as a gift for Dr. Sugita.