Thor isn't easily distracted. A bit headstrong, yes, perhaps, but always focused, to the point where he learned to ignore even Loki's most cunning attempts at diverting his attention.
So why, he wonders, can't he stop thinking about the way Mjolnir had moved for Cap?
They defeat Ultron quickly, easily, because who has time for plot, and things return to normal— yet still Thor wonders what it is that makes Steve (nearly, he reminds himself, nearly) worthy.
They spar often, just about equal in size, in strength— the only one of his teammates that's true of, Tony dependent on his armor and Bruce on his, er, alternate form— but at the end of each session, he's still no closer to determining how Mjolnir had judged Steve's worth.
(Though Thor watches him lie back on the floor, the slightest sheen of sweat on his skin, shirt tight across his chest, edges of his mouth turned up in a smile as his breathing gradually returns to normal, and thinks maybe he gets it.)
Had Loki known? he wonders that night as he lies in bed, thinking of the way he'd taken on Steve's form to taunt Thor about his extracurricular activities, his love for the humans. He thinks again of Steve's hands on him as they'd fought, the way they'd moved together so smoothly in battle against Ultron, and feels himself growing restless, desperate for an explanation— or maybe something else entirely.
He knocks on Steve's door.
Steve answers in nothing but his boxers (tight, too tight, just like all of his clothes), sketchbook and pencil abandoned on the bed behind him. "Thor. Hey."
"Did I wake you?" Thor asks, voice rough around the edges. Steve shakes his head. "No, I—"
"Good." Thor places a hand on his chest and presses, firm, until (because he knows his own strength, knows Steve's own strength, knows he could push back if he wanted to, but) he takes a step backwards and allows Thor to pull the door shut behind him.
"What is it?" Steve asks, and he sounds so concerned, of course he does, and Thor clenches his hands into fists because everything Cap does is just another explanation he doesn't want to see. "I was hoping," he says, his eyes on Steve's face, "that you could tell me.” He keeps his breathing even, steady. “How did you move the hammer? What is it that makes you worthy?"
Recognition dawns across Steve's face. "Oh! That— that's what this is about?" He chuckles. "Thor. Buddy. I think you're making too much out of it. I couldn't even lift it, remember?"
"But it moved," and Thor may love the humans but their inability to grasp the significance of this frustrates him to no end. He lets his gaze slip down Steve's body, searching for explanation or distraction, he couldn't (wouldn't) say.
Steve notices. "Is that really why you're here?" he asks, and his voice is softer this time as the backs of his knees hit the bed. He sits, leans back, looks up at Thor like a question, or maybe an invitation. "Or is it...?"
Of course it's something else, has been something else all along. Thor has always been attracted to strength, to the passion and willingness to fight for what one believes, worthy or otherwise. (He thinks of Loki, shoves it aside, because he's gone, because he has a new lost cause to look after, now— himself.) He's found himself admiring Natasha on more than one occasion, even the Son of Coul for his single-minded dedication, but Steve— Steve is the tip of the iceberg, and Mjolnir moved for him, and Thor knows exactly why his pulse is racing. "Finish your question."
"Well," Steve says, uncertain, almost shy, (almost worthy), but he's not looking away. "You are the only one who can match my strength..."
Thor goes to his knees.