Kara had a beautiful childhood, she was like other kids, had a loving family, had everything she wanted to be happy but that happiness didn't last long. People called Assasins who kill people emotionlessly did the same with Kara's family, she was lucky if we can call that luck, they took her with them..they ''raised'' her, she was just 2 years old, all she saw was nothing but bunch of computers and robots comunicating with her, teaching her things that would not cross her emotions, for 22 YEARS she had not seen people anywhere, just technologies which had created a MONSTER.

She didn't know what Love was, she didn't know what Happiness was, why is even a person smiling? that's totally strange for her. All she does is to kill, kill & kill.

There's an organisation against Assasins, they catch them and kill because it is almost impossible even to try calling out their human emotions, they were just like robots. Yixing aka Lay is part of this, those emotionless people kill his sister, he has now left to be an only child in family. He wants to protect them, he will do anything to just have his family alive. But what happenes when he falls in love with a ''person'' who he hates the most? Is she going to be perfect for him? won't she cause any harm to him? is she the ONE to be protected?