Your step sis has moved in with you and your wife for the time being, and instead of charging her rent you have come to an agreement that she does the house chores. You and her have a history, and one day when your wife is at work and your step sis is folding clothes she catches you staring at her ass. She suggests that maybe there is a... different way she could "pay" her rent. It doesn't take much convincing until she's sucking your cock just like she used to. You cum in her mouth and after she's finished she makes it a point to say you guys will DEF have to do this again!