Sybilla is a she-cat of Balinese breed with copper-coloured eyes. Despite being a pretty female, her pelt is dirty and poorly treated due the her harsh life. Her features are different from the standard of the Balinese breed: she's slightly shorter legs, her ears are missing the proper beige shade of the breed and her eyes are copper colour rather than blue.
Sybilla lacked the proper standard of the Balinese breed and for this she was supposed to be left in cage to die. The she-cat managed to escape and save her life, finding shelter into the metro stations underground. There she led an hard life, until meeting Francis.
Francis is emotionally involved by the terrible tale of Sybilla's past and convinces her to follow him out from the underground's station. Sybilla remains close to Francis while investigating about the mysterious time running-back event because the same she-cat reveals to Francis of having noticed it.
However, after they find more clues in the archaeological museum, both Francis and Sybilla got trapped inside a moving truck with an human killer.
After the man is accidentally killed during the fight with Francis, Sybilla reveals to be herself involved into the conspiracy and attempts to murder Francis after revealing that the time running-back event involves the whole planet.
Francis is saved by the sudden appearance of Pi, that (for the second time) manage to kill the Francis's aggressor, putting an end to the life of Sybilla.
As for Max and Sigmund (and Bluebeard in an alternated time-line), Sybilla is one of the non-black terrestrial cats involved into the Brotherhood of the Black. It's likely, due the hard life of Sybilla (provided that his story was not a lie, but there is no hits in the novel that she lied) that the she-cat has been fascinated by the possibility of a new life in Chronos.
At the end of the novel, the death of Sybilla turns to be a never-happened event due the intervention of Chronos's cats. It's likely that Sybilla kept on her miserable life in the underground but it's left unknown if Francis will try to meet her again to convince her to came out. Anyhow, Sybilla is going to remember nothing of what happened.