Bratty Rave Step-Sister JOI

You promised to take your step sister to a rave, its all she's been talking about for weeks, you're both good to go until you see her outfit, it's barely a piece of string! She insists its what all the rave girlies wear, but you're not convinced, and you start getting hard while looking at her. She notices and tells you to touch yourself while she shows you even more...