Does the reason they were there really matter? For Kyon, anything that could have kept him in the clubroom would just be a pretense. For Yuki, his asking her to stay before the others arrived was more than enough.
"..." She stares at him. Even she can tell he is different in ways raw data can't define. The book is closed, in her lap, her hands folded over it, but she does not move from that chair. There is no way to calculate the optimum scenario, so she does not act.
It reflects on him, driving him mad. For every second she sits still, he has let a day pass bearing it, gone a week carrying everyone else's weight. Everyone's weight but hers. The only one who had ever lifted that mantle. It wasn't that she'd go so far as to remake the world for him, just that she would spare but a second to see him. Refuge. Release. He was done being paralyzed.
"Yuki," he says as though struggling for breath. Not Nagato. Yuki. This is not lost on her. Nor is his approach. Closer. Closer. So close. They have been this close before, but never this...close. He is down on one knee before her, his hand touching her face. "Yuki," he repeats, and all at once the data comes flooding to her. Heat, tension in the sets of muscles...
He's shaking all over with anticipation, and he thanks God her skin is so cool because it's the only thing he can focus on through the surging warmth. Has she ever looked this beautiful before? Yes but he has never appreciated it more and he fights like a madman to keep himself under some semblance of control because frankly, it's just bad etiquette to throw a lady on the floor.
Oh, he'd had his dirty thoughts before. About Haruhi. Mikuru. Tsuruya. But this was different. This was Yuki and someone so pristine deserved gentle and thoughtful treatment and...
He lunges in and presses his lips against hers. He savors those small lips, gripping the frame of the seat so hard his knuckles turn white as he balances his shaking body over hers and damn it'd be so easy to just let himself fall and conform to her shape but easy now, Kyon, easy.
"Suzumiya Haruhi would react unfavorably if you pursued this course of action." She had barely passed his back when she felt his hand grasp her wrist tightly. She stopped, turned to face him. With the difference in their strengths, it was a futile gesture, and yet...she could no longer move. She saw in his eyes something entirely unique. His teeth ground together, oh her acute ears heard them, felt the muscles in his other hand ready to tear from clenching such a tight fist.
"You're not Haruhi's babysitter!" he snarled. "Neither am I. Your only job is to observe her, so...observe her! But I want this." He stood staring at her for such a long time. She did not move, and God was she perfect in her stillness.
"..." Silent. Of course she was. But it wasn't a no either, so...
"Yuki," one last time. He did not slowly draw her close to him. He did not gently caress her face. She did not see gentleness in his eyes. She saw a mirror of pure want, and as he fiercely pressed his lips against hers once again and pinned her to the table with his hips, she accepted him and all of those broken feelings that came rushing into her. He grabbed her into his arms and held her tight with craving, jealousy, frustration and love, and she could feel his fingertips through the cloth over her back, pressing red that white, snow-like skin. He urged himself harder against her, making the table screech in protest as it withdrew from their pressure.
He pulled away when he'd given her the fire, and realized her eyes had been open the whole time. He laughed. Yuki briefly wondered if he was malfunctioning. When he'd let it out and the haze was clearing somewhat, he took a fresh look at the alien girl. She understood nothing of what he was doing. Yet it was not mindless acceptance. She felt it too. This was willing submission. That perfect doll-like beauty...
"...belongs to me," he whispered, somewhat out of breath.
"I thought you'd never ask," he joked, and scooped her up into his arms. She was incredibly light; that he nearly ended up sending her skyward made him clutch onto her all the tighter as he turned and pressed her back against the wall. Her face was impassive, but he noticed she was moving. It was a mechanical sort of fluidity, mathematical in a way, as her arms traced their arc upwards to place her white hands upon his shoulders and her legs worked themselves about his waist, locking herself upon him. He wondered at this for a moment, wondered if she had anticipated this moment somehow. She had no instinct to—oh, but she did.
"...optimal," she said flatly, unblinking. So, then...
"You want this, Yuki?" he already knew the answer. But he wanted to hear it. Needed to hear it. He was selfish for her.
"...That is correct."
He nodded, leaned in and kissed her neck, breathed hotly upon it, placing his hands on her waist and beginning to work slowly up her shirt, each finger tracing a different contour of her back, filling his whole mind with sensations of her.
She made no sounds of pleasure, nor suddenly became human. She remained the strange simulacrum no matter how far they carried the journey. But she accepted him for all his human failings. He accepted her for her otherness. She will never call his name or cry an animal cry of pleasure. The word 'love' will always remain unspoken.
But somewhere between perfect and so fucked up, they understand.
And they can accept that.