Can be from anywhere
Spoilers regarding Shikabane Hime (If you don't care, please read anyway.)
I held a grudge against her after she attacked Ouri too heavily and felt that she deserved it.
Nozomi Kasuga being ripped apart and crushed by a Shikabane during an escape. It was later revealed that she wasn't able to return as a shikabane despite having regrets.