Minato is surprised to realize that Kakashi has grown up. It was almost as if he expected Kakashi to stay in that awkward half grown stage between adolescence and puberty. He didn't expect to see Kakashi's gangly, bony limbs to fill out, slender, but with muscles sliding under a velvet layer of pale skin. He hadn't expected Kakashi's voice to change, the high, almost scratchy pitch smoothing out to a lower, mellow register. He hadn't expected Kakashi to grow, now standing nearly as tall as himself.
Kakashi is definitely no longer a child, and Minato is also quietly disturbed when he notices how... sensual Kakashi has become.
He's leaning against a tree, watching Kakashi go through a standard kata. He made the excuse "to check your form", but he knows that Kakashi's forms are perfect, and it's not why he wanted to see the kata. As Kakashi slides between the different forms, he's all long limbs and deadly grace. His student moves towards him, Minato can see more and more.
There's a fine sheen of sweat shining on Kakashi's brow, a physical manifestation of his effort. Sweat makes the dark blue of his shirt darker; the dampness making the cloth cling to Kakashi's lithe torso. Kakashi leaps up, twisting in midair air, and the shirt hitches up, exposing a sliver of pale stomach, muscles rippling under a thin layer of skin.
He's panting by now, Kakashi openly, as he flawlessly executes the last few forms of his kata, Minato tries to make his subtle, tries to make it istop/i, because it's iwrong/i…
Kakashi stops in front of Minato, leaning forward, panting heavily. Minato can see beads of sweat rolling and dripping down his student's neck, soaking into the already damp material of his collar.
Wincing, Kakashi stands up straight, clutching at a stitch in his side.
"How was…that, Sensei?" he asks, still gasping slightly. His voice is low and smooth, the syllables seeming to slide off his tongue.
"Perfect." Minato murmurs, his lips caressing the word, reluctant to let it go.