Kamui had come to expect a lot of things from Fuuma -- verbal torment, physical torment, and he'd already received both from the older teenager in their latest standoff. It was why he found himself pressed up against the souther-most wall of the library, one wrist trapped at a painful angle and held against the wall above him, his head still swimming slightly from the impact that had slammed him into such a position in the first place.
It's not until Fuuma's pulled away that the fog clears enough for Kamui to realize that Fuuma had just kissed him, and it makes Kamui stare up at the older teenager with a mystified expression on his face. It's not until Fuuma quietly laughs that a deep, belated blush rushes across his face, and it's not until Fuuma speaks -- "We should continue where we left off, 'Kamui'." -- that the young Dragon of Heaven suddenly remembers that he's still in one of those dangerously precarious situations that tends to end with him nursing broken bones.
He manages to (mostly) focus on the fight after that, but later, as he lays in a bed in the hospital, he can still recall with the heat and intensity of that very brief moment with annoying clarity. The memory stays with him all night long, even once he's fallen asleep.