If Kaku really had to guess, he would probably say that it was when he was about 16. He'd been watching Lucci fill out paperwork; he was in one of his rare and surprising placid moods, and seemed to be his own world (although, thinking back, it was probably someone else's world that he was borrowing, or had stolen, or likely killed its owner to get, because Lucci's own world was never that calm). He'd also been eating an apple– and Lucci was the only person Kaku had ever seen who could make an apple look like a symbol of original sin while eating it– and had tucked his hair behind one ear to keep it from falling in his face while he wrote. The black ink suggestion of a tattoo was visible under the edge of his sleeve, and Kaku, sitting across the room and failing to do his own paperwork, found himself not only unable to look away but actually wanting to tear Lucci's shirt off so that he could see the whole tattoo and run his hands over it and the scars that adorned his back and through his hair, his hair, and just shove him back into the couch he was sitting on kiss him absolutely senseless and maybe bite the ear that the hair was tucked behind and then he had needed to get up and leave the room.
Of course, it could have been before that. It could have been when he was 12 and having his first training session with the other future Cipher Pol members. He had met Lucci before, but the older boy had never so much as glanced at him; then, there Kaku was, watching the instructor demonstrate some sort of technique he couldn't even remember, and had caught Lucci looking at him. Not staring blatantly or furtively glancing, like the children in Kaku's old village had in curiosity and horror at his nose, but looking. Watching. And Kaku had met his eyes and found something dark and overpowering in them, and had been forced to look away, but for the rest of the day (the rest of the week) his nerve endings would crackle with anxious energy whenever he thought about it, and it took years for the hairs on the back of his neck to stop standing up when Lucci glanced in his direction.
Yes, maybe that was the start of it. But when he was 16, that incident had probably been what drove it home. Drove what home, Kaku would ask himself, and then the part of him that wasn't in denial would answer, The fact that you are desperately, terrifyingly, unnaturally and wrongly in love with Lucci, and then the first part would answer back, a bit ruefully, Right, that's it.
Kaku wondered if he ought to be annoyed or grateful that Lucci had waited until Kaku was 18 to molest him; he had concluded that he had only waited to frustrate him (because, damn him, he'd known from the start), but that didn't make it any easier to decide on an emotional response because he never knew whether or not he should give Lucci what he wanted.
To this day, Kaku didn't know how Lucci had found the key to his room. He had probably picked the lock in a manner undetectable to human senses (he wouldn't put it past him). But anyway, he had gotten in and surreptitiously locked the door behind him and hidden, lying in wait like…well, a leopard, until Kaku returned from the day's training, exhausted and aching and just wanting to sleep, but it was not to be; the moment he stepped into his room and found the light switch not working, he knew something was gravely wrong.
Even by tuning all of his senses up to maximum and setting his Soru response to "hair trigger", he didn't stand a chance. The only sound of attack was a muffled thump as Kaku's back hit the wall and his wrists were pinned above his head. The room was dark but for the faint, pale glow of moonlight through the curtain, and the silhouette of his attacker was hazy and ill-defined; there was a gust of breath on his face that smelled like apple, and Kaku's thought process promptly fell into a sharp pattern. Apple, Lucci had an apple for lunch, he usually doesn't, that's why he did it, so I would know it's him, why an apple? Did he notice that time? I hope he didn't notice that time why am I concerned about that when Lucci is pinning me to a wall why is Lucci pinning me to a wall why did he cut my light why am I still thinking.
He tasted like apple, too, and his lips were crushing and his tongue was determined and Kaku's mind was blank and foggy and as soon as he realized that Lucci was very calmly and steadily unbuttoning his shirt a hot spike of electricity shot up to his brain from the base of his spine, he shuddered, Lucci broken away and laughed (low and rumbled and dark) and bit Kaku's neck just a little bit too hard, and Kaku's mind shut down entirely for a long time thereafter.
Lucci's hands were hard, but not rough, and they moved with purpose; Kaku wished he could see him, but all that was visible was a vague outline and a square of ghostly light over the suggestion of a shoulder. Kaku hadn't realized how quickly this was having an effect on him and would have been ashamed of himself when Lucci found out exactly how well this had worked if not for the fact that he was too busy inhaling sharply and biting his lip and squeezing his eyes shut.
Kaku kept wondering what he was meant to do with his hands, but it didn't matter because very shortly it had gotten to the point where all he could figure out what to do with them even if instructed otherwise was hold on, nails digging hard into Lucci's shoulders, but that seemed to be good enough. Also, he found that he couldn't stay quiet; he kept gasping and mumbling things that probably didn't make much sense and weren't really meant to almost under his breath into the curve of Lucci's neck, and a few times he might have moaned, or possibly more than a few times.
Lucci never made a sound.
The door clicking shut afterward, however, was the loudest sound Kaku had ever heard in his life, aside from the blood rushing in his ears and his own panting and the thump of knees on carpet when his legs decided that they had had enough of supporting him for one night.
He had been worried, perhaps ridiculously so, that it had only been a one time affair, but a few nights after that it had happened again, and a few nights after that, and a while after that Kaku had waited outside Lucci's door for him to come back from a short mission and Lucci had let him in without a word, as if he had been expecting him, which he probably had been.
Five years, Kaku sometimes found himself thinking, slightly mystified, and this was still going on. They were partners, a team, practically a force of nature. Unbeatable. And they were together, both of them, him and Lucci and it made Kaku's head reel. The funny thing, he realized, was that while neither of them had ever committed infidelity unless it was for work purposes, Lucci had likely– almost certainly– been attracted to other people before, but Kaku couldn't think of ever wanting anyone but Lucci.
He wondered once, briefly, if that was what it was like to have a soul mate, but the notion was soon dismissed because in order to have a soul mate ones' lover must have a soul.