Chapter 1: Toothbrush

Koyomi Araragi had just recovered from brushing his sisters teeth in their weird dare game after his other sister Tsukihi barged in on them. Tsukihi had yelled at them and run off in search of something to beat them with, so Koyomi was left alone once again with his sister Karen, the tall and tomboyish one of the fire sisters. As he looked over to her to try to find a way to weasel out of his promise to have her meet Kanbaru, He was surprised to find his sister staring at him. The deep grey pools of her pretty eyes made him feel that weird feeling he had earlier, while brushing her teeth. Karen caught herself staring however, and quickly looked away.

'Crap, I hope Karen isn't upset with me, I might've taken it too far…' He thought.

He turned to Karen ready to apologize to her, but Karen seemed distracted, He didn't really notice his sister's sad expression before. Her eyes were staring at the floor as she lightly stroked her lower lip with her index finger, which had now creased into a pout.

'Is she sad Tsukihi interrupted the dare?'

Karen then looked up at Koyomi, and Koyomi had felt his heart stop.

'That gaze she's giving me is so strong…' Koyomi began to clutch his chest, feeling nervousness seep in.

He felt a feeling of wistfulness radiating from her…but maybe…her eyes were beckoning too?

'Little sister…what kind of signals are you sending me?...I better say something.'

"Ha! well…" Koyomi started, snapping Karen out of her stupor. "That sure was an intense competition Karen! You sure withstood me pretty well…my respect for you only grows!" Koyomi smiles.

"Nishi-shi! My admiration for you only grows Onii-chan!" Karen beams confidently, "You make my blood run hot with your challenges!" Karen replies in kind.

The two begin to laugh together at their silly activity, until their laughter dies down, and silence begins to permeate as they stare heavily into each other.

Karen was the first to break the silence.

"W-we can continue, I-if you want Onii-Chan..." Karen whispered.

The siblings then begin to move from their seats.

Almost in silent mutual understanding, Koyomi and Karen Araragi fell into each other's embrace, ceasing to be brother and sister, or even individual entities. They were now something else entirely as they melded together, one united form!

'Like the robots in those Super Sentai t.v. shows.' Koyomi thought.

Koyomi and Karen then plopped down on his bed together, and their legs had tangled into each other, as Karen pulled into his chest, and lay her head against him. Koyomi wrapped his arm around her, as he stared at the ceiling.

"Are we...the KoyoKaren Araragi Justice Force United Robot Now?" Koyomi raises his hands in an imitation of a karate fighting robot.

Karen let's out a small laugh and gives him a warm smile,

"I guess Onii-chan, hahh!"

Karen let's out a startled squeak, making Koyomi jump.

"Y-your hand..." Karen stuttered.

"What?" Koyomi asked.

"It's on my butt..."

Koyomi gives her a wide smile.

"That was on purpose!" He exclaims proudly, hot air leaving his nostrils.

"That's my Onii-chan, so brave and daring! How dangerous."

Karen gives him a quick glance, before he can register what kind it is, he feels her hand cover the one on her behind.

"Ooh!" Koyomi's brain alights with adolescent hormones rushing through his body.

Karen smiles at him again, her mischievous smile stirs a funny feeling in his chest.

'A flutter? Butterflies? What's up with this feeling? I'm just laying here with my sister, like we always have.'

Just then, Karen squeezes his hand, making him, by effect, squeeze her butt.

"Ah!" Karen groans playfully as she keeps squeezing, ensuring Koyomi gets a firm grasp. Koyomi's hormones are on fire and he feels the nosebleed coming, his mind starts swimming.

"Onii-chan..." Karen whispers, Koyomi can hear the beckoning in her tone.

Karen turns over, placing one of her long slender legs on either side of him, and begins straddling him.

"Onii-chan…touch me more..."