How many times have you watched an anime series, and when thinking about it, there was one (or more) character who was there, and supposedly important, but who doesn't do anything? A character that made you think to yourself "why is he even there?"
As for myself, I think that Leo Scorpse from Scrapped Princess fits that bill. He is there, but he doesn't have any real purpose in the plot except to serve as a taxi service for another, more interesting character. He's supposed to be a knight, but he doesn't do anything in any battles except stand around, it seems.
Heck, there was one character who was better in every way than Leo who didn't even get a name until the series was almost over.
Who do YOU think is the most useless character that anime has yet provided us with?