Thanks for sharing!! Pretty neat Why does complement not work for you?
If I grab some Chinese characters from wikipedia: it seems to work:
chars={"?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?","?"}
partchars=chars[[;; ;; 3]]
Complement[chars,partchars]