One of the most tropes EVER!
(Excuse the quality on the last two. I don't know how to make them pretty)
I gasped when I saw it the first time when Lucien told Klaus to kneel. Seeing it in Guardian was a happy surprise. On Love in the Air I was waiting, anticipating it to happen. GAP was unexpected and the softest execution EVER (the only time it's not the villain directly telling the protag to do so)
Shows:
Guardian (Shen Wei)
The Originals (Klaus Mikaelson) (not romantic but still)
Love in the Air (Payu)
GAP the series (Sam)
Features:
Strong, powerful, arrogant character brought to their knees
Usually forced by others into it
Kneeling is a sign of submission but they are not submitting to the bad guy pre se, they are doing it coz they love their person more than they hate the bad guy.
It hurts me but it's one of the best shows of devotion.
To Paraphrase Shahrukh Khan in Kuch Kuch Hota Hai -
A man bows his head to only three people. Mummy, God and....
(he never finishes the sentence. Lover is the word, Rahul. But that was India in 2004, so more likely wife.)