Info Dump:-
**The Ashes of the Damned**
It was a weapon developed and used in the "War of Superiority".
It is known to enter into a person's brain and manipulate them into committing bodily harm to themselves and to others while giving the host some extra super strength and some additional super-quirks
They feed on the brain tissues and the blood vessels but don't necessarily kill them.
Getting eaten by these ashes does not exactly kill the person getting eaten because their eaten parts are put together and reanimated into their complete self in another dimension - The Mystery Dimension. In that dimension, they actually get eaten by the 'real form' of the ashes which live and thrive in the dimension while sending their off-springs to other dimensions. This process actually kills the person for real; No further process.
These ashes are rumoured to be actually a specific race of conscious creatures originating from the Mystery Dimension, and their primary goal is to bring their 'Master - The Saviour' to Earth's dimension and provide the humans as his food. But it is just a rumour- for now.
Other than the humans and their brains, these ashes also consume the bacteria and chemicals present on rusted metals, which went on to be used as weapons to sacrifice humans to the ashes.