In the spur of the moment

You finished up with your hair and quickly started washing your body with your back to Lucy, occasionally turning around to check what she was doing but the only reaction you got was her eyes flicking down to cock. A grin formed on your face whenever you caught her but you mainly left her alone as you waited for her to come to a decision.

With a final quick scrub down, you moved away from the stream of water and out of Lucy’s way, making sure to brush your dick against her ass this time as you went past. She tense up for a second when your erection was between her cheeks but calmed down when that was as far as you took your teasing.

“I’ve made my decision” Lucy quickly declared, trying to dispel any hint of nervousness from her voice.

“I’m sure I’ll be delighted with the change” you sarcastically responded, giving a hand motion for your sister to continue.

“Well, considering you barged in on me, I think it's only fair that I get to come in whenever you're having a shower from now on” she announced with a smug grin.

To be honest you were expecting a lot worse when you had given her this option but you weren’t about to tell her that.

“Really? It was a one-time accident and you expect me to…” you complained, trying to act like this was more of a punishment than you actually thought before getting cut off.

“You better expect it. And for mouthing off you're gonna have to… let me watch you cum right now!” she replied, rushing the last part as she excitedly made it up on the spot.

Your erection twitched in response to her demands and you tried not to reveal your inner thoughts. You still found it strange that the punishments she gave you were the same as the rewards you wanted but maybe she was looking for some plausible deniability towards liking what the two of you were doing. You were certainly happy with what she suggested but if she wanted to carry on the act she was putting up then you weren’t going to stop her. At least, not when you were probably about to jerk off in front of your sister again.

“Fine, fine but you know I can't cum on command right?” you asked, doing a bad job at sounding dejected.

“Of c-course! Now quick turn around” she stuttered, confusing you with the command.

You did as she asked and faced away from her, the water from the shower only hitting your feet as you were far enough away from the spray. Nothing happened for a few seconds until the soft sensation of Lucy’s skin was felt against your back. She had pressed herself against you and you could feel her tits sandwiched between you. You saw her head poking over your shoulder and you were expecting her to just watch you from close up when her arm went around your side and she grabbed hold of your erection.

You stood there with your mouth slightly open in surprise at the unexpected help. She had seemed shy just a moment ago but apparently, her enthusiasm had won over her hesitation as you could make out a look of joy in her eyes as you turned your head to the side. Lucy blushed slightly when she saw you staring but quickly acted like she didn’t care.

“Knowing you, you’ll probably take ages to get this over with so I’m gonna help speed this up. You got a problem with that?” she spat, staring back at you to make sure you didn’t have a reason to refuse.

You had no reason to disagree with her anyway so you just gave her a quick nod as she tightened the grip she had on your cock. She lacked Sarah’s caution from when she had first given you a handjob but she still gave you a few slow strokes as if trying to figure out what you liked best. Considering she was in her first year of college you assumed she had some experience and the supposed ‘boyfriend’ that you had heard her speaking to over the phone.

Knowing that she was doing this for you while she might technically be in a relationship brought something a little extra to your excitement but the fact that you had your sister playing with your cock was amazing in and of itself. A groan escaped your lips as she sped up to a more comfortable pace. With her standing behind you, you had little to do with your hands and ended up bracing yourself against the wall while Lucy did all the work. She kept herself glued to your back and you could feel her nipples poking you now that she was getting more excited.

If that wasn’t enough to turn you on, her breath was heavy in your ear as she kept her chin resting on your shoulder, diligently looking down at your cock as she worked her hand up and down your shaft.

“W-when are you gonna cum already?” she stuttered, her voice cracks betraying the angry tone she was trying to use.

“Well, it would help if you stopped telling me to hurry up” you replied, still confident enough to reply without getting distracted by her handjob.

“Oh really? So you don’t want me to tell you how much I really wanna see you cum, and how good it will feel to cum all over your sisters hand” she teased, trying to get a reaction out of you.

“...I didn’t say that” you admitted, getting more excited just as Lucy wanted you to do.

“Ha, keep dreaming pervert” she said in response, not seeing the irony that she was the one jerking off her own brother in the shower.

She sped up once again and under the constant stroking, you found yourself getting closer as the minutes went past. You knew you couldn’t last long and reached your tipping point when Lucy started to mumble close to your ear about wanting to see you cum. She seemed to not realise that her desires were leaking out but the whispers only seemed to spur you on even more. You removed one of your arms from the wall and tapped her leg to warn her you were close.

“I’m gonna cum” you announced through gritted teeth, trying your best to prolong the pleasure while Lucy seemed to hear your words as a challenge, speeding up the movement of her hand.

“Come on, come on” she whispered, urging you on and causing you to finally stop holding back.

Pleasure raced through you as your first rope of cum arcs into the air before landing on the floor. Lucy kept on stroking as she watched you cum, aiming your dick slightly and bringing her idle hand round your other side to try and form a cum to catch the rest of your cum. Your arms braced against the wall stopping your legs from giving out and your body tingled as Lucy coaxed more cum out of you, her hand still wrapped around your cock and she seemed to be having limited success with collecting your cum with the other.

“Yes, come on more” you could hear Lucy whisper, spurring you on.

Your orgasm continued with a final few shots, the pleasure starting to die down to manageable levels and Lucy's hands now overflowing. Both her hands were coated in your cum which seemed to bring a smile to her face as she finally let go of your dick, bringing her hands up towards her and watching the cum drip down her arms.

You stayed like that for a minute as you caught your breath, only moving when Lucy’s seemed to break her concentration and remember that you were still in the shower with you.

“Right good you can leave now” she smirked, happy to have got what she wanted.

“At least let me clean up first, I know you only want my cum but at least give me some courtesy” you teased back, getting a click of her tongue in response.

You walked past her, making sure your dick fell against her thigh and wiped the last few drops of cum that Lucy had missed onto her. Lucy knew what you were doing as you took a few seconds longer than you should but she made no comment in the end. You quickly cleaned up and got rid of the rest of the evidence that may have still been left on the shower floor before brushing past her for the final time, making sure to miss the wet patch you had just created before.

You were sure Lucy would have shoved you out the door if not for her making sure your cum stayed on her hands. You took your time getting out of the shower before realising your chances of getting caught by Mom would increase if you lingered for too long. Rubbing yourself down with a towel left you dry enough to not drip when you went out into the wall, turning around before closing the door behind you to see Lucy was still staring at you.

Authors note:
Seems like there have been a few milestones almost back to back recently but KDK is now in the top 50 sci-fi stories on this site :D.
Thanks for all the support and hope you all continue enjoying the story.