Kirk strode onto the bridge that first day, and each of the bridge crew stood to attention. He made his rounds, strong arms laying relaxed at his sides, a smile on his charmingly boyish face, introducing himself in-kind to each officer and shaking their hands with both of his own.
When he got to Spock, the effect was almost immediate. He sensed it as Kirk approached, that nameless pull that almost shocked Spock into stepping toward the man. It wasn’t a scent so much as it was an instinct– a sixth-sense that Spock recognized immediately, if only because he had met so many people and he’d never felt this before.
Source: Ardor, by ThereBeWhalesHere – Star Trek [Archive of Our Own] | https://archiveofourown.org/
AU in which Vulcans recognise compatible mates by scent, this is 90% Spock longing for Kirk and 10% insanely hot smut. All while somehow managing to sound completely plausible and in-character.