I'm looking for a kdrama I saw in a MV on YouTube once

Would you be able to post a link of the MV here as well as roughly what time the drama appeared? Might help if the scene can be seen. Click reply, then the weird square with characters in it to the right of the forward arrow and to the left of the spoilers alert button, then click insert then reply and that should do it.

The Korean music video you're describing is likely "A Midsummer Night's Dream" by Park Hyo Shin. In this video, a man in a suit and glasses is shown alongside a woman in a traditional Korean hanbok, with scenes interweaving between modern and historical settings. 

 emeraldarrows:

Gunman In Joseon? FL wears a hanbok and ML wears a suit and glasses after his return/for the remainder of the drama.

I think Gunman in Joseon may be right