Mina Tatebayashi

Mina is a half-mermaid half-vampire youkai. She's 5 years old and is under the care of Shidou after their parents got tuned in an incident not long after they were born. Unlike her twin Kana, her blood is closer to a mermaid's, and her body grows into a teenager size (with no boobs, at least in the manga, unlike Kana) if she gets covered in water. Another difference is that she is incredibly outspoken and brash in her speech, and speaks in a Kansai dialect.