My step sister's alluring undergarments and sensual tits enticed me

I had no idea what was in store when my magnificent stepsister flashed up at the gym, unveiling her perfect backside and appetizing bumpers thru her see-through lingerie. As I fought to fight back her seduction, she deftly gave me a mind-blowing forearm job before railing me rock-hard in both cowgirl and switch sides cowgirl positions.