She suddenly pulls her own top off.

Her smaller boobs are so arousing you instantly feel that tiny tong turning wet. The hand you’ve put in front for protection suddenly is a liability, not only bringing a bit of rub to an overtaxed pussy, but also drawing attention to your predicament as the telltale wet mark grows.

She notices and bites her lip. You feel insanely attracted to her… she’s your sister… but it’s not your body… it’s not really ****, right? You should say something but you can’t really help yourself. You start rubbing your pussy through the tiny undergarment, your breath quick and shallow. Hers is now the same and she pulls you in for a kiss… not a sisterly kiss, a sexually charged kiss that has you both dizzy with desire.