Iron Widow

Zetian has a vendetta, and she's willing to kill to get revenge for her sister's death.

In the future, male pilots fly mechas and are partnered with female concubines. From them, they can draw power through a psychic link in order to battle an alien race on the other side of the Great Wall that is threatening to take over their city. Many young women die as a result, but not Zetian. She turns the table on her assigned pilot and takes control, but she quickly decides she's not satisfied with merely getting revenge; she will take on the entire system, learn its secrets, and expose it for what it truly is. What she doesn't count on is the conflicting feelings she has for two men who are complete opposites of one another. If you're looking for an original science fiction novel with a strong female lead, romance, and plenty of battle action, be sure to read Iron Widow.