He enjoys trying on her underwear

He is about to come out of the closet
He just doesn't know it

Harry enjoyed dressing as a girl

Harry slipped on the leopard pattern panties and felt a thrill shoot right through him. He pulled out the matching leopard pattern bra and slipped it on fastening it expertly at the back. This wasn't the first time he had worn his sister's underwear and he had no intention of it being the last.
Every opportunity he got he would steal into Maxine's room and head straight for her walk in wardrobe.
Inside it was a crossdressing wonderland with pretty lingerie and sexy clothes from floor to ceiling. Harry knelt on a chair and practiced being a pole dancer in the mirror. He loved dressing as a girl and having a sister who enjoyed wearing such sexy clothes was a big bonus. He even kept a blond wig to wear for when he was dressing.
Outside the closet Maxine slipped quietly out from behind the curtain with her camcorder in her hand. As she watched him prancing about in her undies unaware he was being filmed she whispered quietly to herself.
"Oh yes, you do look so cute in those panties, just wait till all my friends see this video."
She had suspected her brother was a sissy for a while but now she was going to get all the evidence she needed to finally get him out of the closet.