It happened in headquarters.
Lavi was following Kanda back to his room, and chatting up a storm. Kanda had already snapped a few times for the idiot rabbit to shut up or fuck off. Despite that, he kept rambling on, still called him Yuu-chan, making more veins in his forehead pop.
Kanda reached his door and was holding the handle but immediately about-faced to yell at the idiot some more for prattling on, but he froze. Lavi was now just a few inches away from his face. Just a second ago he was several feet away.
Lavi grinned and laughed at catching Yuu off-guard. Another vein popped in Kanda's head, but before he could shout a thing, Lavi interjected,
"Yuu-chan is cute when he's annoyed."
Which only caused him to freeze again in shock. He didn't have words or phrases prepared to counter these kinds of actions. Lavi started leaning toward Kanda's face. It couldn't be for anything other than a kiss, and that's when he unfroze and abruptly flailed, shoving Lavi back so hard that he tumbled over the railing. He was barely hanging by his fingertips over the seemingly endless pit down the middle of headquaters.
"Yuu! It's your fault if I die!" Lavi yelled at the top of his lungs.
Kanda proceeded to grumble at these circumstances, glared at Lavi a little longer than he needed to, rolled his eyes, and strode over and grabbed the idiot rabbit's wrists to pull him up.
"Thanks, Yuu." Lavi smiled
Kanda merely growled and was about to insult the idiot some more when Lavi interrupted him.
"You owe me."
"I owe you?! I just saved you!"
"It doesn't count when you're the one who almost killed me!"
Kanda grumbled again, extra long, before finally muttering, "what do you want?" with a tone of disgust and disapproval.
Lavi grinned ear to ear. "It's easy Yuu! You can do it RIGHT here." Kanda said nothing but his eyes narrowed. "Let me have a kiss and we're even!" If looks could kill Lavi would be dead a dozen times over in that moment. "wellllll?"
Still saying nothing Kanda just crossed his arms and closed his eyes in a huff. He opened one eye to glare at him once before closing it again and standing in his tensed position, a snarling expression on his face.
Lavi took that as Kanda-speak for, "fine, get it over with." Lavi got as close as he could possibly be to Kanda without actually kissing him. They could feel each other's breath on their faces. Kanda's eyes were still closed tight.
"Thanks, Yuu." Lavi said quietly with a kindness to it.
That brief pause made Kanda open his eyes a little in time to see Lavi looking at him like he'd never seen before. It was only for second because then Lavi closed the distance, pressing his lips against Kanda's.
The mild shock Kanda felt from the pressure caused him to uncross his arms, and Lavi took full advantage to press up against him with nothing in the way. When Kanda felt the door at his back, like a reflex, his hands landed on Lavi's hips, and he started to, a little, JUST a little, kiss him back.