You're shook. What should you do? Your sister could walk by your bedroom at any moment. Then she'd see two naked girls. You're paralyzed and unable to act, but then you realize you start getting out of this skin. You reach for your back.
It's too late. There in the doorway stands your sister with a shocked expression.
After an initial shock, she turns around, probably to not stare too much at your nakedness. With her back turned, she asks: "Who are you guys?"
You look at your girlfriend. She looks back and whispers: "It's your sister. You handle it." She shrugs, leaving all the responsibillity to you.
You feel your stress level rising, especially as when you're this girl you're especially vulnerable to stress and anxiety. What should you do? You feel such shame over your dirty sexual deeds, your girl-self finding just the act of sex and nakedness too crude to share, but then there's the whole thing of you and your girlfriend stepping into much younger girl skins, which you don't want to be judged by. Still, The only option you can think of is just coming clean.
"It's me, your brother," you say meekly. You're barely able to speak, and as this girl and with her tiny nervous voice, you're anything but convincing.
"You know my brother?" she replied, having misheard you, maybe because of the ridiculousness of your statement.
You look at your girlfriend, unsure of what to do, hoping she could assist you
"You got this," she whispers to cheer you on.
You do your best to gather all of your courage, and to speak clearly.
"No it's me." you try again. "I am your brother." I am just wearing a skin suit." You feel silly saying this. You realize there's no way she's going to believe you without a practical demonstration. You fiddle with your back and grab your zipper. "Look. Look at me."
She turns back towards you with a sceptical expression. "I'm not following you. Is this some sort of prank?"
You pull at your zipper, opening your back. You pull your skin's head off, and reveal your original self from the shoulder up. "Look," you say in your normal adult male voice.
"Eek!" she shrieks and jump back in reaction from horfor, but after the initial jumpscare, she doesn't seem scared.
"Bro? That's you? for real?" she seems excited. "It looked so real. Put it back on! Let me see!"
You do. You grab the now lifeless head hanging off your chest, and put it back on.
"OMG," your sister exclaims. She stares at you, but then she looks at the girl next to you, your girlfriend. "Who is she? Is she also someone wearing a costume?"
"Yup," your girlfriend replies and steps off the bed. "I'm his girlfriend." Unlike you, she seems completely calm about this, to the point where she's able to proudly stand in front of your sister as a naked thirteen year old girl.
"No way," your sister reacts. She looks at your girlfriend, and points something out, "But you're so much shorter." She then looks at you. "You step off the bed too."
You do, and then your sister stands in front of you, being now a full head taller than you. She again studies your body, looking at you closely from your toes to your face, staring at you right in your eyes. You feel a bit uncomfortable as you're checked out by this taller "older" girl. You feel very anxious about your nakedness, and how close she's looking.
"How is this possible?" your sister asks.
"It's like magic," your girlfriend explains. "You could try one too. Look there." She points at each of the two thirteen-year-old girl skins laying on the floor that you didn't pick. "You could try one yourself."
"Can I?" your sister exclaims. Her vision darts between the two skins. "Which one should I choose?" she asks.
"Whichever you like," your girlfriend shrugs.
Your sister picks up each of the skins to compare them. She looks at each of them meticulously. "I think I'll pick this one." She holds up the black girl skin. "She looks the most different, like from how I look, so that might be fun I think. But what do I do now. Do I just put it on, or do I need to do something more?"
"Basically," your girlfriend replies. "Just get naked first. So unless you wants to give me and your bro here a show, just go somewhere else, and put it on. That's it."
"Cool. Okay. I'll do that." Your sister then darts away, probably towards her room.
"God," you exclaim, feeling a sense of relief with her finally leaving. It could have gone much worse. You were afraid of accusations considering you two were young naked girls together on a bed. Even with the room smelling like sex, she didn't comment or insinuate anything about your very precarious sexual situation. At least she didn't know about more skins existing, so you don't yet have to explain exactly why you chose to become middle-school-aged girls specifically.
You feel yourself getting touched. Your girlfriend lets her hand walk across your stomach. She then gives your breasts a teasing poke. "You know what this means. Maybe we'll have a new member for your harem." She giggles.
"She's my sister."
"So?" she laughs.
You really do hope she's joking.