Runa has been a friend of Seto San since her childhood years. Actually their families are something like neighbors. As you may guess, Runa is also from the mafia. She uses her mermaid voice in order to be a music idol all over the world. Lunar is very popular among the girls and boys and is their hero, and Michishio is one of her fans. When she finds out that San is in Saitana town, she cancels all her work and goes right into the city. She is often accompanied by her two bodyguards. Lunar has a “favor” to return to San and nothing can stop her from avenging San. In an accident Michishio discovers Runa’s identity. Because of the circumstances, Lunar starts living in Nagasumi’s house. And she even goes to Michishio’s and San’s school.