Hanahaki that isn't based on love itself but can come from other emotions
Instead of it originating from lack of interest in the other person, the hanahaki forces someone to actually confess, reciprocation of feelings isn't required to cure someone, hanahaki would be caused by the repression of emotions
Essentially, hanahaki is just your body telling you: actually tell them how you feel, you idiot
Hanahaki can come from many emotions: anger, love, hate etc... The flowers depend on the feelings, the amount varies depending on how intense the emotions are.
Asters for love, aconites for anger, among other things. Five flowers being coughed up are usually cured by vague posting online about the other person, ten flowers can be cured via indirect confession, but more than fifteen flowers have to be cured by directly confessing to the other. More flowers = more extreme the confession.
Flowers that represent worry are more common during times of plague, while love flowers would be more common during times of peace. Friendship flowers are the most common types of flowers.
Hanahaki can be dangerous but easily manageable so long as someone can afford the right medicine to avoid flare-ups, in more extreme cases the victim is either encouraged to go get surgery, which has the side effect of numbing any emotions for the other person, or to just confess
When a person dies, it's traditional for people to cough up grieving flowers and collect them to be used as decoration for the person's grave.