Grin and Bare Him by Cynthia Sax

This cyborg will be the warrior his female requires.
Cyborgs are designed to fight. That is their primary purpose and 98.2356 percent of the manufactured warriors enjoy battle. Tremendously.
Grin, a K model, is one of the rare exceptions. When he escaped his cruel creators, he set down his sword and allocated his processors to less violent pursuits. He projects he’s left his war-waging planet rotations behind him forever.
Then he meets his beautiful, beguiling female, the one being he’s destined to protect, to claim, to love for all eternity, and his plans for peace are completely decimated.
Mohini needs a ship.
She has a dangerous mission to complete and the first step in that assignment is arranging transport to an enemy-controlled planet. The vessel she has set her sights on is guarded by the sexiest cyborg she’s ever seen.
To gain access to his ship, Mohini is prepared to kiss, caress, seduce the muscular male. The mission is her focus. The pleasure she experiences will merely be a bonus.

A female has to do what a female has to do to save the universe.
Grin And Bare Him is a Cyborg SciFi Romance set in a dark, gritty, sometimes-violent universe.
It features a humanoid female undertaking a dangerous mission, a cyborg intent on keeping her alive, and an enemy with enough firepower to blow up an entire sector.