WARNING(S): Um...
Yaoi? Yon(d)kaka/Minakaka
Underage? Though that is free to interpretation since ages aren't mentioned beyond "Older/Elder" and "Younger/Junior".
Mine
The very first thing Kakashi noticed was that he was bound- mitts, that allowed his hands to barely open beyond a fist, secured together at the wrists and tied off above his head- though his legs remained free for him to stand.
The second that he was naked.
After that came the realization that he couldn't see, his headband pulled down over both eyes and tied securely enough to act as a blind fold. His mask was gone but in it's place was a strap that wrapped around to buckle close behind his left ear and pushed a gag, like some twisted overgrown pacifier, securely into his mouth. A collar encircled his neck, tight enough that it pressed insistently against his skin whenever he turned or tilted his head- a leather leash hanging loose from the collar, it's handle swinging dangerously close to his privates.
Before he could do more then tense his body in panic, an achingly familiar voice barked out a sharp "No." at him, freezing him.
'Sensei?' His startled question came out muffled and garbled beyond recognition from the gag, he snuffed repeatedly to ascertain himself that his kidnapper was indeed his former teacher- a good way to identify people as only he knew just how good his sense of smell was.
He was ignored as the Yondaime spoke musingly, "The Yellow Flash's Pet Hatake." His nose wrinkled at the nickname had been dubbed with since he first started accompanying Sensei on missions, earning a disapproving 'tsk' from aforementioned man.
"Everyone is aware of who you belong to- everyone except you. And I," He could imagine the wicked grin that stretched the blonde's mouth. "I decided to remedy that and show you that you are mine."
The possessive growl made him shudder in very enticing ways, a flicker of arousal shooting through him as he recalled the multiple...propositions made to him from either gender since he reached puberty that he turned down on the seemingly vain hope that Sensei would be his first. Not that he was innocent, ANBU were required to go through training with the seduction corps after all, he just never had sex.
That arousal, it seems, made itself known visibly, earning a deep throated laugh of amusement that made him squirm uncomfortably and wish he had his mask to hide his shamed flush with. When the older man spoke, speaking in a tone as if stating a simple and well-known fact, Kakashi froze again, "I. Own. You."
"First, I was your friend." A hand, left from the placement of the thumb and pinky, rested so that the tips of the fingers prodded the bottom of the collar on his neck.
"Then, your teacher." The fingers pressed and curled, blunted nails pushing against skin.
"Guardian." The thumb curled around the leash, making it bump against his half-hard penis.
"Commander." Another hand, right, took hold of the leash and held it out of the way as the left slowly scraped it's way downwards.
"Partner." He sucked in a breath, nearly choking on saliva when he forgot the gag, as the fingers paused at his stomach to teasingly allow one tip to wriggle against his bellybutton.
"Hokage." The hand continued down, carding confidently through his pubic hair.
"And now, I plan on being your lover- understand?" The hand gripped him and he moaned as best he could when it lazily started to move.
He let out a startled, yet muffled, yelp when the leash handled slapped against his nipple with swift efficiency, "You are to answer when asked a question. Do you understand what it means that I plan on being your lover?"
He nodded slowly, groaning appreciatively when the hand that had paused continued pumping his cock, "Good boy."
He wanted to be angry, he was not a pet to be reprimanded then praised for doing tricks, but the familiar feeling of satisfaction that he got whenever he earned Sensei's approval welled up.
'Oh god.' An almost sick feeling churned in his stomach as he wondered if, all this time, he was being trained.
He shuddered in something akin to shame when his cock twitched approvingly at the thought. He wanted to be disgusted, to be furious- he had always prided himself on his independence, most eight year olds wouldn't have been able to live on their own as he had- but couldn't. This was Sensei, his captain, his Hokage- all the people whom shinobi were taught to obey and he was a damn fine shinobi.
Another yelp earned from a second abused nipple drew him from his thoughts, "It's rude to ignore your Hokage, Ōkami-sama."
The use of his ANBU name as the hand moved, those blunt nails lightly scratched against sensitive skin, made him feel all at once aroused and dirty.
Ōkami-sama was ANBU's leader who could and did challenge the Hokage's assignments for the ANBU who couldn't. Ōkami-sama was unyielding, unmovable and unflappable.
To be called that now made Kakashi feel vulnerable in a way that being bound, gagged, blinded and fondled didn't- it was, he assessed with mute mortification, both exhilarating and intoxicating.
He wasn't aware that he whimpered until Sensei let out an approving sound, "Oh, I like that- let's see if we can't get you to make that sound again, hmm?"
Then he was let go and nails digging into his sides, scraping down to his thighs and forcing him to stand with his legs spread slightly. A puff of warm air and-
'Oh god, Sensei!' He let out the strangled lovechild of a moan and whimper, earning a chuckle who's vibrations made him let his head fall back as much as he was able and sound his appreciation as best he could. All too quickly, under the sweetest tortures of a warm mouth and insistent tongue, he felt his body start to tense in anticipation and Sensei swallowed which was too much for him and-
Kakashi sprung into a sitting position in his bed as his chest heaved in exertion, felt the damp spot and collapsed back onto his be bed with a long, drawn out "Fuuuuck!"
A/N:A Wet Dream. Because teenage hormones are abound and Minato is arguably the person 'Kashi cares about the most.