It's another way of spelling kewl, but better.
-The origin of kewz-
Yami: That is so kewl! K-E-W-Z!
Heket: Umm... Yami, that spells 'kewz'...
Yami: Well, kewz is greater than kewl! Muahaha!
Cooler than Cool. Something that can only be described by a word that Yami can not spell.
OHMEGAWD! That movie was so KEWZ! K-E-W-Z!