A lot of the Canterlot High students have always thought Rainbow Dash was more like a guy than any other guys at school, She ate dirt and was rough on the sports fields, she guzzled soda after fighting with the machines for the can, and frankly, she's tired of being mistaken for a dude. So she goes to two of her friends, asking Rarity and Sunset what makes them feel like girls and if they can help her. It won't make her any less of a person, to feel more like a girl.
Teen and the sex tag is for some references to older age appropriate content, E.X. mentioning their femininity and some mild sexual or similar references, but this isn't a clopfic and there's no strong sexual content.