What kanji is this, and what's its meaning? In the anime Moribito: Guardian of the Spirit (精霊の守り人), when the Star Diviners are speaking and do not wish for the contents of their conversation to be heard, they say something like "There is no-one else in this room." or "This room has only empty vessels." (depending on the translation, I guess). Then, these other guys in the room (generally people who only light candles and the like) pull a piece of cloth that hangs backwards from their 'hat', and cover their faces. This piece of cloth has a symbol, that I guess is a Kanji (I do not know many kanji, so it is only a guess).



What Kanji is this, and what is its meaning?
It isn't kanji.  The character you see here, and others, were invented for this particular TV series.  They're called ヨゴ文字 ("yogo moji"), and this character in particular is a substitute for the kana む ("mu").

See the following charts for details: kana and numbers 

As for what it means, given the context in your question, I would guess the む on his mask is 無 ("nothing").

(As an aside, these characters remind me of Tangut script.)