The story/plotline is really messy.  I had my doubts about this drama because of the whole time travel thing, and my doubts definitely weren't gone after watching this.   The drama lost focus throughout and it felt like there really was no central theme the drama was trying to portray.  This wouldn't have mattered as much if the drama compensated for it in other ways, comedy etc., but it didn't.  In fact I've little to no idea what I was supposed to have gotten from watching this.   The writers almost scratched the surface of different issues but as soon as it seemed they'd go somewhere with it, they'd stop.One thing that I always hope when watching a kdrama is that it will not only provide interesting and deep main characters, but supporting characters who are eye catching and attention getting as well.  That's one of the many areas that this drama fails in.  Bo Hee is the most boring character ever.  Drill is also boring which is ironic because I think he was supposed to be the fun and quirky friend but instead he was just annoying and one dimensional.   The grandpa and Mal Sook could have been really cute and interesting but they weren't given enough backstory for me as the viewer to care about them.  I also felt that the focus shifted from the supporting characters all of the sudden to just a couple of the main characters rather suddenly and nonsensically.  This wouldn't have bothered me as much if I was super into the main character's storyline, but I'm gonna be honest, the main characters really weren't a whole lot more interesting than the supporting characters.  Yoon Shi Yoon's character, Da Bong or Yoo Hyun Jae started out cute, but as episodes went on he started bothering me more and more.  Kim Min Jae's charcter Ji Hoon had potential to be intriguing.  I liked his whole struggle with choosing his life's path at the beginning  when he wanted to debut even if it wasn't encouraged by those in his family but instead of developing that, the writers just dropped that and chose to start ignoring Min Jae's character.  He became the guy who had a crush on the girl and nothing else really happened to him.  MJ, played by Eunwoo, I probably liked the most but his role was really small and he didn't get to do much.  The main couples romance didn't seem natural and I didn't feel the chemistry between them.  Kiss scenes kind of cringy in my opinion.  I think I shipped MJ with Woo Seung more than any of the other guys.  Obviously there were parts to this drama which I liked otherwise I wouldn't have forced myself to finish it.  But I would not recommend it and I almost regret watching it, but not quite.