I don't know Korean, so this is what a get from the raws. I'm not sure of the details but the big picture is that bellow
Gbb We see the and of her story on the war with Polar Bear, that go from them trying to kill each other for her saving him from assassins. At the end the school it's bombarded, and she try to safe at least someone, a little girl, but the little one doesn't survive and she is heavily injured and it's send back to Korean
For some reason her sister visits her. It appears they had a deep conversation, but I didn't get nothing
The 2 ML tells her more about the past of the Polar Bear, we discovered he had a sister. She liked photography and was really sweet.
On my interpretation for her safety, he always keep a distance from her. Even if that hurt them both. At the end both of them leave the country, but she was envolve on a cara accident and died. It appears the accident was fabricated by the political enemies of the ML, and the 2nd ML knew.
Oh. The 2nd ML had romantic feelings for the little sister.
The MC sisters is kidnapped and they want Polar Bear life for the garante of her safety. She goes to his room with the pretext of change his curative and sacks her weapon. Polar Bear wake up and manage to steal her weapon, but contrary to expectations he is relative calm. He gives her a knife kept under his pillow and sacks one for himself. That's how it ends.
They appear more close during this time. A long time friend of the ML even notes on the first sight there's is something between them, and especially that he's change around her.