This a trope that you see fairly often. Someone gets held captive by someone else and falls in love with that someone else. Who each of those are varies, but the trope itself is fairly common.
For this particular prompt, who each of those people are is well lain out. The one doing the capturing is the supervillain and the one being captured is the love interest of the villain’s enemy, the superhero. Since this involves superheroes and supervillains, they may very well be called that by the general populous and if they are, they may very well not be exactly that. Of course kidnapping someone is never a nice or okay thing to do especially given that the supervillain’s stated reason is to use the superhero’s love interest against them.
On the other hand, it is interesting to note that the supervillain has seemingly not done anything otherwise cruel to the love interest while the love interest was in their custody, unless the love interest is into that sort of thing, which is not really implied here at all. Likewise, the love interest has not left the superhero for allowing this to happen so often and there is no indication that the superhero has done anything to make the love interest feel more safe. It is possible that this is just an illusion based off the fact that they keep getting taken or that such an option was offered and rejected. The love interest may want to live their life without the intrusion of a body guard or may feel that although they have not been injured when taken by the supervillain, a bodyguard might be. Or maybe they just like being taken by the supervillain seeing as they do ultimately fall in love with them.
We simply do not know what the cases is that allows the love interest to keep getting taken by the supervillain. There are just too many possibilities and that’s what makes this so useful as a prompt, you can come up with solutions that fit your story. At least so long as your story includes superheroes and supervillains.
Another thing to keep in kind is that the point-of-view character doesn’t have to end up with the villain. They can, if that’s what makes sense in your story, but this could be a tragedy where one of them ends up dead or it could be the story of how the superhero finally ended up with their love interest for good as they find themselves having to fight for the love of their life before they break apart for good. A character who falls into love can fall out of it, if it makes sense. And the love doesn’t have to be real either. They could just be in lust, though that doesn’t seem to fit the prompt. They could be getting close as friends and mistake it for love. They could pull the supervillain out of villainy, end up working together as villains, or realize that the supervillain was the hero, or at least the anti-hero, all along and kidnapping them was to keep them out of the clutches of the superhero who was the one doing the really bad stuff.
Since it seems to be from the point of view of the love interest, maybe we only know what they know and some of what they know is wrong. Maybe the love interest doesn’t actually know that the supervillain is the supervillain, because secret identities and all that. Maybe what the superhero sees as kidnapping the love interest sees as someone they know who keeps making them late to things. It could actually be kidnapping, but they don’t realize it and by the time they do realize it, they have already started to fall for the supervillain and things are just complicated. Do you think they know what’s going on and do you think the rolls are as clearly established as they seem in the prompt?