Mechagodzilla X Female Godzilla

Her might is unmatched, yet he is made to match her. Humans can't rely on her forever, and so they need their own weapon. Mechagodzilla. Made from the remains of a deceased relative of the Godzilla species, Mechagodzilla is powerful enough to get rid of the kaiju threat to humanity, and hopefully even Godzilla. What they didn't expect is for him to come to life. Now alive and sentient, Mechagodzilla has only a single want: destroy all monsters. But through the purpose of his new body still lies that Godzilla relative.

It's obvious they'll fall in love, as that would be defeating the purpose of the story if they didn't. The interesting part is the how, and what lies between hate and love.