Flowers for you

Deku suffers from a rare disease known as Hanahaki. It is a mental disease as much as it is a physical one-the sufferer's feelings of lost or unrequited love physically take root in their lungs as a flower. Everyone's flower is unique, growing with the diseased person's feelings until it blooms through the throat, obstructing the airway and killing them. There is no cure except for the love being returned. This is not a guarantee, though. Oftentimes, the object of the afflicted's affections is deceased. The grieving lover dies a lonely death, becoming the flowers at their own funeral. Other times, the partners reunite but the flower is too far along. The couple dies in each other's arms, exchanging breathless kisses of rancid petals.