Shirahoshi

Shirahoshi, the Mermaid Princess (人魚姫) is a very large smelt-whiting mermaid and the youngest of King Neptune's children. She was first mentioned by Pappug, claiming he knew her and even promised to introduce her to the Straw Hat Pirates when they arrived at Fishman Island (though later this does not appear to be the case).

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 her room, where Princess Shirahoshi was sleeping. Luffy was unknowingly walking on her stomach chest. When she woke up, she became greatly distressed.