Legend has it that there is an ancient race who are initially born without gender distinction, and choose their own gender according to their own wishes after the red oath ceremony. The gender is mostly determined by the first person they fall in love with. It is said that most of them are slender, enchanting and charming. When they cry, their tears will turn into pearls, and the silkworms they produce will not soak in water. That ancient mythical race is the Sharks.