Ryuunosuke, is a girl, who dresses like a boy, acts like a boy, looks like a boy and fights like a boy, but all she really wants is to be like a girl.
When Ryuunosuke, was born, her father really wanted to have a son, to keep the tradition of running the family restaraunt, when Ryuunosuke's mother died, he decided to raise Ryuunosuke as a boy, because of that fact, Ryuunosuke doesn't know how to act any way, other than like a boy.
Ryuunosuke's goal in life, is to wear a girl's school uniform, but her father, hangs it over her head, and says that she has to beat him first, before she can wear it.
Ryuunosuke, and her father always fight, in the episode that Ryuunosuke is introduced, Ryuunosuke, and her father destroy their restaurant, so they pack up, and move to Tomobiki, and Run the school store.
All of the girls, are in love with Ryuunosuke, even after she tells them that she's a girl. Ryuunosuke's got more girls chasing after her, than Mendou does. Which makes Mendou quite jealous.
On top of having all those girls hitting on her, she's also got Ataru hitting on her, Ataru who always seems to have a keen eye for a babe, hits on her regularily, just like he hits on every other girl in town.
The name Ryuunosuke, is a name only given to boys, to add to the irony of the character.