The Five Elders possess the ability to spread Incurable Diseases
Ginny was the East Army commander of the Revolutionary Army, having joined the group alongside Bartholomew Kuma 22 years ago, back when they were known as the Freedom Fighters. She was previously a slave who was forced to take part in the Native Hunting Competition on God Valley 38 years ago.
In a certain country, Ginny and the East Army had planned to meet up with Kuma’s group. However, she was captured. She ended up becoming a slave again and was forced to marry a Celestial Dragon.
Ginny eventually contracted a deadly disease, the Sapphire Scale disease, and died.
What happens is that the disease covers someone’s skin with blue stones once they are exposed to natural light. This is whether it’s the sun or the moon. As a result, their skin also hardens like stone.
Unfortunately, there is no cure for the Sapphire Scale disease in the One Piece universe.
My theory is that the Five Elders are basically “Starscourge”. Each of them has a gem-based (likely off-world in origin) disease that kills those infected.
Ginny’s disease wasn’t mentioned, known or even speculated about before she was captured and hostaged by the Celestial Dragons. Which means Bonney got infected while she was a hostage and married to a Celestial Dragon. I think that Ginny got infected by Saturn (yes, I do think Bonnie is his daughter). And I think Roger got infected by one of the Five Elders as well.
We’re going to eventually get a MASSIVE Laugh Tale flashback ending with Roger vs the Five Elders. And while Roger will win, it’s going to be a pyrrhic victory since he’s going to get infected by an incurable disease.
To add: Luffy will suffer the same fate after reaching Laugh Tale. But this time, Chopper will cure him thus fulfilling his dream.
*Theory by Su_Impact