"We're going to put on a show for you"

Of course you know what she means, you just can't believe she means it. Katie is kneeling next to Tess's chair now. Both girls give each other confident glances, and then turn to smile at you.

You freeze. You have no idea what to do. You sense that your mouth is hanging open in dumb shock, but your cock is starting to stiffen at thoughts that you still aren't quite convinced are about to be your reality.

"You really have made my sister very happy." Tess says. "I've never seen her this happy. You deserve the best birthday present ever." As she speaks Katie reaches over and brushes her long brown hair off her bare shoulder.

You've seen Katie touch her sister dozens of times, casually, familially. You never thought you'd see it done sensuously.

Still you're frozen. You can't think of a damn thing to say.

"I'm not sure he's getting it." Tess chuckles.

"Then let's do a better job of showing him what we mean." Katie responds, leaning toward her sister. Sure maybe they have a few differences here and there. Katie's jaw is a little stronger. Tess's flesh is a little more pale. But if a stranger were to see them next to each other on the street, they wouldn't need to ask if they were sisters. And now, sisters enveloped in a passionate kiss. Their tongues intertwining with one another. Saliva, deep breaths, sibling love, and whatever this is.

You lean forward in your chair. You're still not certain what you're seeing is real. But you certainly have no plans to take your eyes off it.

They finish slowly, smiling, blushing a bit and turn their attention back to you. "See we made a decision that tonight was going to be a special night. Things are going to happen tonight that will never happen again and that have never happened before." Katie says.

"Well that's happened before." Tess interjects.

Katie rolls her eyes playfully. "Yes, we did that a few weeks ago just to make sure we could go through with this without freaking out."

"Right." Tess echoes. "It was just as nice this time."

"Thanks" Katie chirps. Their banter is like two people who have been around each other all their lives. "Now" She looks at you knowing she's shocked you more than any other living person on this planet. "What would you like us to do?"