For as long as she's been aware, the heroine, without a single relative, lived under the care of the state. Both of her parents' faces were unknown to her.
In front of this heroine, a boy appeared.
The boy's name was "Hikaru." It appeared that he was the heroine's twin brother, separated at birth. He had a proposal for the heroine: "Could you go to school in my place?"
The heroine was shocked by this crazy suggestion.
Furthermore this was an all-boys school—the only high school in the prefecture for delinquents.