Mutual Masturbation with Step Sister: Naughty Help

I still think about that afternoon whenever I hear the floorboards creak upstairs, because mutual masturbation with stepsister was never supposed to feel that natural, but there we were, her sprawled on my bed in those tiny shorts while I tried to act casual and failed completely. She asked for help like it was the most normal thing, and I watched her fingers move slower than my heartbeat, tracing little circles that made her bite her lip. I mirrored her rhythm without thinking, my own hand working in time with hers, and when she let out this shaky breath and said “don’t stop,” I felt my whole body tighten. Her legs parted a bit more, and I could see how wet she was getting, glistening under the lamp light. We kept eye contact the entire time, neither of us willing to look away first, and the room filled with the quiet sounds of our breathing and skin moving. I came before she did, and she smirked at me, like she knew she had all the power, then finished herself off right there while I watched, completely wrecked.