Void Killing Words

Q: Seeing as how Shiki wasn't able to kill words, I'd like to know, how far does her capability to understand death actually extend? <The Red Loser Isn't a Loser!>
Nasu: Well, it's just a rule of thumb, but if it's the normal Shiki then she can kill everything that physically decays. The thing with words is that she doesn't regard their death as "decay" but rather "fading into oblivion".
Takeuchi: Ah, so it's a problem of recognition, then.
Nasu: Of course, that realm of recognition is already no problem at all for the inhuman Miss " ".

Kara no Kyoukai Movie Pamphlet Q&A Chapter 6 – "Oblivion Recorder"