The first time Spirit kisses Stein, the meister doesn't realize what's happening until it's over.
They are at home, framed in their most common orientation: Spirit stretched out along the length of the couch, half-focused on the book in his hand, feet angled awkwardly sideways to make room for Stein sitting more normally at the other end. The meister is investigating a textbook too heavy for his lap, twisted far sideways so he can lean over the table at his right that is supporting the weight. He could get up, move to the dining table or lock himself in his room, but even the painful press of Spirit's knee against his hip doesn't entirely counteract the invasive pleasure of the physical contact, and besides he's used to it by now (he tells himself). There's no point in moving when the payoff would be so minimal.
Stein is truly reading, lost in the words on the page in front of him, so it takes him a long time before he realizes that Spirit isn't and hasn't been for some time. When he glances away from the page at his partner, the older boy is watching him with an expression Stein doesn't fully identify, and his grip on the book in his fingers is visibly loosening, putting the book in danger of being dropped.
Stein is still half-thinking about bone and tendons and ligaments, but part of his mind has been tuning itself to Spirit's less easily interpreted body language, and that part is pulling apart the weapon's expression in an attempt to categorize the component parts. He is biting his lower lip between his teeth, that is worry, and there is the quirk of a smile at the edge of his mouth, that's amusement, or mischief, more precisely; there is usually something to worry about when Spirit looks that way. His forehead echoes the concern his teeth are exhibiting, and his shoulders are angled away in the same hesitance, but his arms are tense with something that Stein can't quite get a read on - determination? conviction? - even when the book completes its stalled tumble to the floor.
"Spirit?" Stein offers without further details. Usually this is enough to push the weapon over into some sort of minimal confession - Spirit seems to need permission to speak, or perhaps reassurance that Stein is listening, before whatever fragile dam he has erected on his emotions shatters in the weight of the flood. This time Spirit lurches forward so he is almost sitting up, draws back to lean on his elbows as that panic flares stronger. With the lamplight behind the meister's head Stein can see the illumination catch Spirit's eyes, turn them infinitely blue with reflected light. Spirit's eyes have always been uselessly complex for the meister - he can never get any helpful data from them because there are always dozens of emotions vying for expression in them, and every time he tries to extract information he ends up getting distracted by the color, how can anyone's eyes be so clear, it defies rationality, and then they both look away rather more flushed and hot that Stein is at all comfortable being.
As he is now, he realizes at a great distance. Whatever details were safely spinning in the back of his head have quietly exited, leaving his mind entirely enthralled with deconstructing Spirit's expression, and now he's lost in that blue again.
Spirit's fingers close on Stein's glasses before the meister sees them coming; what he gets in cleared vision he pays for in lack of peripheral awareness. Then his glasses are gone, the distant edges of the world gone blurry with the lack of focus. Spirit is still close enough for clarity, though, and Stein is starting to feel what he would describe as 'nervous' if he had ever felt such instead of watching it play across Spirit's face.
He wants to speak but he doesn't know what to say, and Spirit's expression is really starting to unnerve him. The weapon's eyes are going dark, Stein realizes, the dark pupils encroaching on the blue and there is a singular emotion there, perfectly clear for once, but Stein's never seen it before and doesn't know what it means. Spirit breaks eye contact but only to look down and he is looking at Stein's mouth, that makes no sense at all, and then the weapon is moving forward faster than Stein can react and his lips are against Stein's, and Spirit is kissing him, that makes less than no sense. There is no time to react, no time to process, really lips are just like any other skin but so soft, there's almost no resistance there at all, and then Spirit's mouth is gone and he is fitting Stein's glasses back on before the meister has caught back up to events.
The smile is there for sure now, pulling at the edges of Spirit's mouth and his lips have never looked so soft before, Stein's suddenly not sure that he's ever really looked at Spirit's mouth before, and this close Spirit must know what he's doing and he pulls his gaze up to Spirit's eyes with a totally foreign self-consciousness that feels strange in his head but meshes perfectly with the blush that is taking over his face. That is fear in the weapon's eyes now, fright at the surface but mostly pleasure underneath, and when did his eyes become so easy to read? The nervous shine is fading, amusement is creeping in to take its place, and Stein realizes that this is in response to him, that his face is broadcasting emotions he does not intend and he looks away but somehow that makes the blush worse.
To his infinite relief Spirit doesn't laugh. He doesn't make any sound at all, actually, just leans back as he was and picks his book back up. When Stein manages to look back over, the weapon is doing an excellent imitation of someone really deeply immersed in whatever he is reading in spite of the semi-random smiles that he keeps biting back.
The weapon does blow his cover by sliding his feet into Stein's lap as soon as the meister turns back to his book, but Stein doesn't have it in him to argue or the nerve to turn around to see what expression Spirit is making, so he just tries to drop back into his own mental focus on the subject before him.
It proves far more difficult than he expects.