Its a pretty good drama. The storyline may be a bit confusing but once you watch it more, you'll understand more, This drama had pretty good actors, the characters are also really nice, they have a cute relationship too. I've rewatched this drama a few times now. Overall, the story has two main characters, one is a mono and one is a Probe. They'll tell you what it is later on in the story. Usually, A mono and Probe are supposed to be together. Also, the plot is a bit confusing when it comes to their world, but i recommend.