Gouzaburou Seto

Seto Gouzaburou is Seto Sun's extremely over-protective and loving father. Head of the mermaid Yazuka in the Seto reigion, Gouzaburou is fierce and powerful.

He hates Nagasumi and continuously tries to get Nagasumi killed throughout the series, and takes great satisfaction in fantisizing Nagasumi's death.

He is Sun and Nagasumi's form teacher to look out for Sun during school, but along the way he starts to enjoy his position and maybe even care for his students.