Shirahoshi

Shirahoshi, the Mermaid Princess (人魚姫) is a smelt-whiting mermaid and the youngest of King Neptune's children. She is first mentioned by Pappug; he claims he knows her and even promises to introduce her to the Straw Hat Pirates when they arrive at Fishman Island. She is said to be the one of the most beautiful women in the world.

According to Pappug, Vander Decken IX started sending letters to Princess Shirahoshi once a week and soon, those letters grew into packages. When he started sending threatening marriage proposals, she became so terrified of him that she couldn't ignore him anymore. This angered King Neptune, and his sons gathered an army to find Vander Decken IX.

When the Straw Hat Pirates were taken to the Ryugu Palace, Monkey D. Luffy wandered off on his own in pursuit of food. Eventually, he stumbled upon Princess Shirahoshi, and she became greatly distressed.