This drama started of really good and I especially loved the relationship between the FL and ML (QY). The sci-fi aspect seemed almost irrelevant if it weren't for the fact that the FL was obsessed with finding her 'one' through the message the machine gave before her time travel. But then again the entire plot of the drama was about love litterally being better than immortality. Whilst the FL gave up her immortal life that litterally lacked human emotion to be with her perfect (most suitable/compatible) man, almost every other character in this drama were willing to sacrifice anything in order to gain immortality.

The entire plot of this drama was ironic.
All the "good" guys turned out to be the bad guys and the people that were labelled as "bad" were actually much better than those that thought themselves as good. And the "bad" guys never once labelled themselves as good people, and I loved that about them. They didn't care for labels whilst the "good" guys entire livelihoods seemed to be dependent on these labels.

QY is the ML but he may come of as the second lead for a lot of this drama. I loved that he was the ML, he was the best character in this drama and the most moral despite being described as "devil". His relationship with the FL was the only reason I was able to finish this drama off. The actors had so much chemistry I wish we had more scenes with them.

The FL and ML had a really strange relationship at first. Before the FL knew who she was (after being transported to the past in essentially a doppelganger's body) the ML made her believe they were sibling. But their relationship as "siblings" was the best relationship in this drama, and it was hilarious. The FL thought she had a perverted brother (because he always kissed her) but didn't once think that he might not be her brother. What was even better was watching them pretend to be siblings after the truth is revealed, the chemistry was off the charts. I loved it. Halfway through the drama I'd just skip to their scenes, I just loved the way he looked at the FL and how he treated her.

The SML and the FL had no chemistry. I hated the fact that the story went back and forth between the two guys. The plot started to drag halfway through because of all the useless back and forth. At some point even started to hate the FL for the way she treated the ML who was always by her side.

I was really satisfied with the ending. Would have been better if it was extended. I waited the entire show for that ending and I got it. I read that the book ending is better and longer.