Banner of Souls by Liz Williams
In the far-distant future a flooded and shattered Earth is governed by the iron hand of the Martian Matriarchy. Martian warrior Dreams-of-War is despatched to Earth to guard a young girl called Lunae from an unknown threat. The clone of an extraordinary heritage, Lunae ages with unnatural speed and has the special talent of being able to alter time.
At the half-ruined city of Fragrant Harbour where Lunae resides with her malignant grandmothers and a member of the genetically modified race known as the kappa, Dreams-of-War encounters a host of intrigues centring on the sinister presence of an alien mission station nearby. When her protege is nearly assassinated, the Martian warrior is forced to flee with Lunae to the flooded northern islands of what was once Japan. But then the child and the kappa go missing en route, leaving Dreams-of-War determined to return to the plains of Mars in order to discover the truth about Martian rule over Earth, and the nature of all the secrets behind it . . .
'Places Liz Williams in the first rank of visionary science fiction writers' Charles Stross
'Liz Williams is this generations answer to Margaret Atwood and Sheri Tepper' Chris Moriarty