Hanahaki, or hanahaki disease, is a fictional illness/disease that anyone can get from unconfessed or one sided love. They will cough petals of their crush's favorite flower, and flowers will grow on their body. If they don't confess their love or the one-sided love doesn't stop, they will die from suffocation due to too many flowers growing in their lungs (which is why they were coughing them)

Fictional means not real btw.