Go look for them

You're still not sure how long it's been, but you're fairly certain that it's been a long time since Nikki and Katie ran off to go discuss something. And it's odd that they haven't found their way back. This intentional exclusion of you on your birthday doesn't seem very festive. So it's time to go look for them.

You head down the hallway and immediately hear the sound of a running shower, and you can see a light coming from under the bathroom door.

So you think you've solved part of this mystery. Nikki must be in the shower. Maybe she just needed a rinse off after a long day, or maybe she spilled something on herself, but she probably just pulled Katie aside to help set her up in the shower. That makes sense. Naturally you decide to leave her be.

Though it doesn't explain where your girlfriend is, especially since it's more than obvious that your bedroom is dark and empty.

So you do something you're not particularly fond of doing, since it makes you look like a puzzled old man, you call out her name "Katie? Katie? Where are you?"

"In here" you hear the response coming from the bathroom.

Alright then, it's Katie who is in the shower. Although that certainly doesn't explain where Nikki ran off to, unless she went home without saying goodbye.

Either way, you don't feel too particularly bad about barging into the bathroom now to ask for an explanation.

But what you see when you do so is more than a slight surprise.

The shower curtain is pulled back and there stands both Nikki and Katie, water pouring down on them, giggling at whatever face you must be making as you stare in their direction.

Your girlfriend is clad only in a pair of very, very, wet panties, plastered to her flesh. Your cousin is completely naked, her pierced nipples, her bald pussy, her tattoos, every inch of her body, currently on display for you to see.

And clearly neither girl minds too much. Katie you're used to being a goofball, but you're not sure you've ever heard Nikki giggle before.

"What is going on here?" You say, more curiously than accusatory.

"I'm not... sure" Katie laughs. "This just sorta happened. Well Nikki sorta..."

"I made it happen" Nikki chimes in, a smile curling across her pink lips. "I made a plan."

Nothing nefarious seems to be happening, but you're still way off from having a satisfactory explanation. "I don't understand" you say, your member thickening in your pants, not needing an explanation as far as it's concerned. "Are you trying to steal my girlfriend?"

"No." Nikki insists "I wasn't trying to steal, I was trying to share. I wanted to... listen buddy I was trying to get into your pants."

This is an unexpected revelation. Nikki, your cousin, was trying to get into your pants?

"Well she thought it might be a thing to do for your birthday" Katie starts trying to explain it. "But I said it sounded a little dirty. Then she said that if she was dirty she should take a shower," Katie stops to think for a moment. "Then I was giving it some thought and determined that it was making me feel dirty... it all made more sense at the time."

And you decide it's time to stop demanding answers, and just go with it. "You didn't want to invite me in?"

"We figured you'd find your way back here eventually" Katie giggles.

"Yeah, but" Nikki adds. "you don't get to come into the shower unless you're feeling dirty. I mean you're gonna have to prove that you're dirty enough to join us."

You wonder if this is what Nikki is always like when she gets horny... playful and cryptic. Either way, you're more than willing to play along.