Manhua/manga/manhwa where the female lead's kingdom gets destroyed, and she's kidnapped and "held hostage"

Question

It was a typical romance isekai to some extent. The female lead read a story and died, then reincarnated into it. She realizes her kingdom gets destroyed (I think). Her sister or someone she knew is supposed to be kidnapped in the story, but instead she gets kidnapped and is “held hostage.” Really, she just stays with and falls in love with the male lead. The last thing I remember is her being “released” and they kiss and she says she’ll come back eventually.

Answer 1

This is Seduce the Villain's Father.

From MyAnimeList:

In the popular web novel Brigitte Wants to be Happy!, Princess Yerenika of Livovny is a side character doomed to a tragic end. But when a woman is reincarnated into the story as Yerenika, she resolves to change her terrible fate and escape death. Unexpectedly, she has joined the narrative at an earlier point in time—both the main characters and the villain have yet to be born!

Yerenika successfully derails the story from its intended course by preventing the abduction of her sister Theresia by Euredian, the king of Bellecourt—a plot point that would have set a series of tragic events in motion. However, Yerenika's plan goes awry when Euredian kidnaps her instead and takes her to his nation. Given that the air of Bellecourt is thick with magic and toxic to Yerenika's weak body, she resorts to her final strategy.

Originally, Euredian went on to marry Lady Soleia Elodia and father Dekalb, the villain of the web novel who led an entire slew of characters to their deaths. Now, Yerenika must rewrite history and prevent Dekalb from ever existing—by seducing his father and making Euredian marry her instead!

A woman dies in a bus crash and is reincarnated as a supporting character in the world of a web novel she'd previously read. Her character -- Princess Yerinica of the small kingdom of Lebovny -- is the aunt of the female lead in the novel, Brizney, who's currently gestating within the womb of Yerinica's older sister, Tezevia.

In the novel, Yerinica's family is ultimately destroyed by the villain, Deckard, who's the yet-to-be-conceived son of Erudian, the emperor of the large kingdom of Belgoat. She also recalls that Erudian is due to invade Lebovny and take her sister hostage in the near future, in retaliation for her father violating an agreement between the two kingdoms.

Yerinica determines that the kidnapping of her sister is a key event which will set into motion the future downfall of her family, so she hides Tezevia to avert this, but ends up being kidnapped and taken hostage by Erudian herself.

Although barred from leaving Erudian's kingdom, she's otherwise treated like an honoured guest there, and sees this turn of events as an opportunity: if she can get Erudian to fall in love with and marry her, then he won't marry Lady Elard -- the evil magician with whom he sired Deckard in the novel -- and thus Deckard will never be conceived.

Yerinica and Erudian gradually develop feelings for one another during her lengthy stay within his kingdom, and when he eventually allows her to return to her own kingdom, they share a kiss and a hug, and she indicates that they'll see each other again.