Shy step-sister desperate to impress

(POV via StepBrother) You & your friend are hanging out when your shy stepsis walks in. She has a crush on your friend but never acts on it. You tease her about it, daring her to show her tits. Desperate to impress, she does! Then you ask to see her pussy. She says no at first, but your friend's compliments makes her pull down her panties. Finally, she's totally naked. You both convince her to turn around spread her ass. She's shocked, but complies. She sees you both have erections. Her shyness turns into kinkiness. She sucks your friend's dick in front of you. Then she fucks your friend and sucks your cock. She doesn't stop until you shoot ropes of hot cum down her throat. After she's done, the weight of the moment hits her. She makes you promise to never tell anyone. She gives you a kiss & wants to talk more about this later...