She evolves from Mermaidyn when fused with a Mermaid Pearl. Her alternate-color form is Mermother.
A fair-skinned mermaid with peach eyeliner and dot eyebrows. Her eyes are dark teal and on the top of her head is a golden fin and turquoise coral accessories. She has black hair tied in a ring and styled into horns on the sides, with a single long bang on the right. Her tail is gold to match her fins "sleeves", with a pearl decoration on her fins, and she wears a shell bikini with a white hagoromo.
Yao Bikuni's name refers to that of a legendary woman, meaning "the 800 years Bhikkhuni".
Once upon a time, a fisherman in Wakasa caught a never-before-seen fish and invited his friends to sample its meat. But when one of them peeked into the kitchen, they saw the fish was actually a ningyo (see Ningyo#Origin), and advised the others to secretly discard the food without eating it. Only one of them, who'd had too much to drink during the meal, carelessly brought the meat home, where his daughter accidentally ate it. It seemingly had no ill effect on her, but when she grew into adulthood and got married, she simply stopped aging from there on. Surviving one husband after another with the passing years, the woman eventually took the habit and began traveling around the world, both blessed and cursed with eternal beauty. She finally returned to her hometown in Wakasa, where she died at 800 years of age.