A mermaid name Mina lives under the sea of Seoul. Mina is the middle child of her 8 sisters of TWICE and she's the only mermaid that is always curious of the human life. One day when 7-member idols, BTS(Bangtan Sonyeondan) was at the beach there beloved Gloden Maknae stoled her heart. Now Mina wants the life as a human, but how is she going to do that