Aileen is the 18th mermaid princess. Her hobby is to research the human world and check handsome chef's social media. One day, Aileen goes to rescue Shi Kyung, who falls into Han River. However, she ends up kissing him. After Shi Kyung leaves, Aileen gets left with the feeling of the kiss and his smartphone. She deter MINes to become a human to meet Shi Kyung again. However, in order to become a human, she needs to go and meet Ahn Ma Nyeo.