Muromi-san

A cheerful mermaid who speaks Hakata dialect. She often goes ashore and enjoys human culture, somehow she feels kindly toward Takurō. However she is incredibly dense, crazy, and clumsy, to top it off, she has a drinking problem. (Source: Anilinkz)

Her age is estimated to be 8-digit but mentally she is only 18. Anyway, don't try to ask about her age in front of her! (age estimation taken from official HP).