They are clearly attracted to each other, even though most of it is subtext. Seul-Gi has a wet dream about Je-Yi and that only proves that she is sexually attracted to her. Je-YI did and said a lot of things that show how she loves Seul-Gi. They don't even have to say anything, the tension is there and very much on purpose (I think the director did a great job with that). It's a mystery show with LGBT themes, it's not going to focus only on the queer aspect. I would say it's not a GL genre, it's just another Korean show which this time has a queer leaning and it's not a bad thing, it's progress. I hope they'll make more shows in this aspect and will be more free in their representation in the future!
This show was nicely done and very creative in its direction. The story while sometimes difficult to understand because of the automatic subtitles was pretty addictive, I always came back for more. One of the reasons to that was especially the relationship between Seul-Gi and Je-Yi, their chemistry was off the charts and credible. I wish they went a little further with the LGBTQ themes, that it was more explicit (not necessarily kissing but through dialogues and such), though I think that the chemistry and subtext were so strong that we all know they were heads over heels anyway. I'm not sure there will be a season 2, but even if they don't make another season, it's safe to say that Seul-Gi and Je-Yi found each other and they'll never let go of each other again; they belong together and that's beautiful. The only criticism I can make is the pacing of the episodes, it could have been handled a little better at times, but it's a solid K-drama with good mystery and acting, so I give it a 8,5/10!