Hear me out on this Hanahaki concept:
Stone has been in love with Eggman since after the first few months of working for him. His feelings of awe and reverence develop into something deeper after he learns all of the Doctor's likes, dislikes, and quirks. He absolutely adores the man.
Stone doesn't suffer from this disease because unbeknownst to him, the feeling is mutual.
The issue? Robotnik doesn't know how to navigate this. He's never had an experience where someone he's been interested in actually liked him back, and it drives him mad. He doesn't treat Stone well, doesn't know how to. He doesn't want to confess, for fear of being wrong about Stone's feelings towards him. Everything in his body wants to make Stone leave or for himself to leave before Stone makes the decision for him, but he can't bring himself to do it.
This ends up being his demise.
As time goes on, Stone's feelings start to fade. Every lash out, every insult, every attempt to make Eggman happy that's met with feigned disdain or apathy chips away at his heart.
Then one day, Robotnik coughs up a rose petal.
It happens after Stone has been employed by Robotnik for 3 years. The Doctor shoos him away to go run an errand for him, after taking his latte without expressing any gratitude. He goes to take a sip of his drink, when he chokes.
He spends the next minute coughing and trying to catch his breath. He grabs a napkin and coughs violently into it, when a bloodied rose petal comes out.
What has he done...