Treat Elena to the toy you were saving: strapon

Elena stood in place, watching Sarah rummage thru the stuff you bought and somehow were set aside. She had stripped after placing the strapon beside her, then was pulling it up. She turned around, Elena still frozen in place "Look at your reward, Elena." she commanded. You could feel her authority over your sister.

Elena turned her head, and while you could not see her face, you could see her shudder visibly. You heard Sarah move to Elena, then Elena was bent over, her face next to your leg. You had a full view of Sarah who was pouring something all over the strapon dildo "Forgot to buy lube, Em." she commented, tossing the bottle to you "Come watch me fuck your sister's holes like the whore she is."

You were on autopilot, moving around Elena, then bent over Elena's hips, getting a good view of her ass, but also you can change so you can see her pussy.

Sarah rubbed it on her ass, the dildo was almost swallowed by her large ass. It wasn't large by most people standards, but big enough to have a jiggle as Sarah slapped it. "Want your reward, Elena?"