The Kitsune Hanyou
When your MC or love intrest turns evil because of the OMGPOWERSOFDoOoOoOM!!! of the Evil Villain, all you need to turn him back is a kiss from his OMGTRUELOVE!! to get him back to his kickass, normal, and good side.
And even though the villain is RIGHT THERE, he still stares and wonders how "That wretched girl" broke through his spell to bring the hero back, while the hero and "The damsel in distress" share a few romantic words and hug and things like that.
Hey, ALL evil villains wait for the love scene to be over BEFORE attacking, can't ruin that good old "*sigh* So cute!" moments, can we?
Of course not, that would be ungentlemenly. All male villains like to pretend they're perfect gentlemen (thus the reluctance to molest the main female character besides mocking her and her friends' useless attempts to defeat him). It's a sign of his evil, how he always pretends to be civil. He never actually means it, and he never thinks it's time to give it a rest already, except maybe when he realizes that his evil scheme has come crashing down around his ears.
Alternatively, if your main villain is a female, she will stay her hand just so she can clap her hands together and give a sarcastic speech about how it's all "so charming. True love reunited, happiness at last. But you realize, of course, that you are doomed! Mwua-hah-hah!" Female villains always like to mock and gloat like that.
And if the villain's neither male nor female, then it's obviously alien and its motives can be chocked up to some quirk or other. (Of the villain, not the
non-plot.)