Lee Minho || Minsung

Jisung goes to high school, he is a shy and quite antisocial boy, he only has two friends whom he looks a lot like. Minho on the other hand is a few years older than Jisung, he is in his last year and is quite "popular".
Jisung is secretly in love with the eldest, Felix and Seungmin know it, they always support him and give him advice, but Han was too shy to tell them, and he was also afraid of not being reciprocated, because Minho had the appearance of being the typical heartbreaker of the school.
One day, armed with courage, he wrote a letter and bought some chocolates. He timidly approached the eldest and handed him the letter, hoping to be reciprocated, but the black-haired boy laughed at him and broke all the words of love into thousands of daddies. Jisung ran away not only because of the humiliation, but he also felt sudden pain in his chest along with nausea. When he reached the bathroom, he vomited and was horrified to see the flowers bathed in blood coming out of his mouth.

Hanahaki is a disease that is acquired from unrequited love. From what I understand, the person is infected by flowers that grow inside the body and expels them by vomiting or coughing. It is fatal since it can lead to death if it spreads. It can be cured by surgery or by the person who initially did not reciprocate feelings for the affected person.