I remember that song from my childhood.
The TV series in unfamiliar to me, but it looks nicely produced with the ancient Korean costumes and settings.
The acting is fantastic. It’s a remake of the same show done as Japanese drama and Indonesian drama, and said to be the best of the 3 versions. The writer of the show is the same one who wrote “Descendants of the Sun” which is a fascinating Korean show that stars my favorite actor, the one who swirls around in this one in fancy outfits, as a special forces officer in love with a doctor who has doubts whether their professions can be together.