Solaria is supporting character in the novel Guilty Gear X Lightning the Argent.
There is no other background information on Solaria except that she's Marina's biological sister. Her singing awakens the Gear cells within the system of the people who drank the Blackard's Vitae and causes them to mutate. Dozens of villagers die mysterious, violent deaths because of this. Later in the story, her singing awakens the dormant Megadeath class Gear Hydra that destroys the village (the people had already been evacuated). Sol finds her, but her innocence stops him from killing her. Instead, he gives her his limiter. After the incident, she comes under the protection of the International Police Force.