the hanahaki disease, it's a rare condition akutagawa unfortunately has. The cause of this disease is when someone experienced unrequited or one sided love, the love grew so much it started growing flowers on your lungs. except those flowers are what's suffocating you. Unless his love was reciprocated, it will not be cured and the person dies instead. akutagawa has fallen inlove with you, but you don't feel the same.

"your affection was all i need to stay alive." he hands out a flower.