The Legend of the Blue Sea
푸른 바다의 전설 (original)
A mermaid from the Joseon period ends up in present-day Seoul, where she crosses paths with a swindler who may have ties to someone from her past.
Starring Jun Ji-hyun, Lee Min-ho, Lee Hee-jun, Shin Won-ho, Lee Ji-hoon, Hwang Shin-hye, Choi Jung-woo, Na Young-hee, Shin Hye-sun, Moon So-ri
Watch "The Legend of the Blue Sea" on Rakuten Viki released in 2016. It's a drama and comedy show, and has a rating of 8.1 out of 10 from Imdb which is very high for this kind of show, and is currently available to watch for free.