Is It Wrong to Try to Pick Up Girls When You're Disguising as a Girl?

Mashiro has a girly name, girly personality, girly body, but he actually is a boy.  Many boys at his school have asked him out knowing he's a boy. Girls are jealous of his soft skin and pretty face. Because of his girl personality and body, he has no real friends. When school ends and summer begins, he's relieved that he has a break from school. Suddenly, a demon interrupts his rest and offers him a contract that can change his life. If he disguises himself as a girl, he can once again live with his long lost sister that he has been searching for his whole life. Demons sole purpose is to be entertained. To this demon, this is entertaining. His mission is to disguise himself as a girl even though he's a boy. If he in any way reveals that he is a boy to his sister or her friends, then he will die a most painful death. What is his decision? If he disguises himself as a girl, what problems will he face?