The main problem is the production and direction, no idea about the acting as they way they were directed boiled down to roughly two facial expressions per character.

The plot is basically a version of What is Wrong With Secretary Kim, but without any humor, or proper direction.
Its starts with how it is colour graded, bland costumes, looks like most of the scenes were shot in a disused modern railway station, there is a lot of walking.

The screenplay and script, There was a story but unfortunately the dialogue was sparse and the silences filled with one of the two facial expressions. A couple of the usual tropes. Perhaps if this was edited to about 8 eps, cut all the repetitive shots, and the making faces like they were sucking lemons, it could have some pace.

My score is for in horse dressage score terms is 5, sufficient, you just went through the motions.