Chuuya has Hanahaki

Chuuya didn't expect himself to fall for you, of all people. To be so in love with you to the point that he found himself breathless.

Or it could be the flower petals filling his lungs that makes it hard to breathe.

“What the hell is wrong with me,” He muttered, coughing again to find more flower petals stained with blood choke out of his mouth. “Damn it,” he cursed, to preoccupied to notice you enter the room.