Assisting my attractive step-sister in getting warmed up

I'm not the typical guy next door, but rather a lucky bastard with a smoking hot step-sister. She's got curves in all the right places and a body that's just begging for attention. One day, I caught her trying to warm up for a shower and I couldn't resist the urge to help her out. I started off with some innocent fingering, teasing her sensitive spots until she was moaning in pleasure. Seeing her writhing in ecstasy was enough to make my own desires flare up. I took her from behind, thrusting into her with wild abandon. The sight of her creamy skin glowing under the bathroom light, her moans echoing off the tiles, was too much to resist. I pounded her relentlessly, my lust for her overwhelming me. The sight of her climaxing, her body shuddering under mine, was the most erotic thing I'd ever witnessed.