Yuuki Domoto was born a mermaid princess she is the daughter to the Pink Mermaid Queen Luchia Nanami and sister to the Pink Pearl Princess Mizu Domoto the day Yuuki was born her mother sent her to the Heartfilia family where she was raised with there daughter Lucy and fakes that she's Lucy's twin considering when Yuuki is in her human form she looks just like Lucy exactly like Lucy. Lucy and her family are the only ones who knows Yuuki is the White Pearl Princess