Your sister in the bath

"Oh, my god!" You shout and reflectively move your hands over your hard cock and your head up to avoid looking at your naked sister sitting in the bathtub.

"Peter, It's fine, I know you were expecting mum but we had a chat and she let me take her place." Stacy, your sister replied. "Get in, the water's lovely.

Still looking away and covering up, you reply "You know about mum and me, since when?"

"Just get in, I will explain, and it is alright to look at me and too late to cover-up I have seen it all before." Your sister replies.

You relax, move your hands and as you lower yourself into the other side of the tub take a good look at your sister. She is very similar to your mum, slimmer but with bigger breast, both have long brown hair and green eyes.

Stacy gives you a good look over lingering on your hard cock. "You creaked the floorboard past my room every night for a week. I watched you and dad fuck mum and heard mum beg for her merman to give her a baby." She explained. "Then I noticed you slipping into the bathe that mum had set running and learnt your signal for merfolk sex. My ex-boyfriend back at Uni was a half-mer too. We discovered our heritage on gap year together. We broke up just before the lockdown hit so I haven't had the chance to find a new boyfriend. Did mum tell you that part of being a merfolk is an increased sex drive?" She asked.

"She mentioned it, yes." You replied, you hadn't been surprised when she told you that. You were always finding yourself in need and since you started fucking you were amazed at how much sex your mum had.

"Well, Mum is currently satisfied and I haven't had any cock since before lockdown so she said I could borrow yours, if that is alright with you?" Stacy preposed. "I can tell from the fact that you are still raging that your answer is yes." She answered her own question.

You simply nodded, you couldn't believe you were going to fuck your own sister. She had been the first woman you had ever seen naked, have spotted her in the shower when she accidentally left the door agar last year. Since then you had a bit of a crush on here. You wonder now if that had been an accident. You were going to bring it up now in case it was and you ruined the mood.

"I'll dunk you if you will dunk me." Stacy stated.

"What?" you asked confused.

"You know to transform, bath sex is so much better as a mer." She explained.

"Oh right." You replied, both being half mer you needed to be held under saltwater to transform. Your sister leaned forward and onto her belly laying dangerously close to your cock. You grabbed her head and **** it underwater. She did not struggle only flinch for a second and then the transformation began. Her legs fused and her tail began to take shape, scales growing and changing colour. She may look like a younger version of your mother in her human form but as a half- mer she was completely different. Pretty pink scales enveloped her legs as they rounded out into a tail and like you, she had no fins and her tail still showed the outline of her feet.