Strive For Forever by Cynthia Sax

This cyborg seeks to vanquish an ancient entity and save his curvy human female.

Euryale made a terrible mistake. She opened a container she shouldn’t have touched and released one of the oldest lifeforms in existence. That all-powerful entity is now utilizing her as its host body and is slowly draining her energy.
Soon, she’ll die.
Euryale has accepted this fate and is determined to use her remaining moments in the universe to save as many lives as she can.
Her plans do NOT include a smoldering-hot, poetry-wielding cyborg willing to decimate entire planets to save her.
While under the control of the Humanoid Alliance, Strive, a K Model cyborg, disobeyed direct orders and refused to kill on their behalf. If he hadn’t escaped their cruel clutches, his defiance would have led to his death.
The male knowingly risked that fate to save the lifespans of complete strangers.
There is nothing he wouldn’t do to protect Euryale. The curvy human female is his genetic match, the one being he is destined to defend.
And she is in danger.
Strive would break every vow, cross every boundary, risk absolutely everything to keep her from harm.
Including battle a deity no one has ever defeated.