The correct spelling is zanpukto with one of those symbols over the "o" that makes it a long "o" sound. However, since I have know idea how to put that in, I just type zanpukto. I know this is wrong, as if you can't put the long "o" sound in you're supposed to replace it with an "ou." So, if you can put the long o sound in, then do that, otherwise spell it "zanpuktou."

Rukia's actually an unranked member of the 13th division. there are some valid reasons for this that are revealed as the story progresses.