I can answer this. I originally had a two characters, but decided to stick with my second one because some friends were on that server. I deleted the original character in-game. Then I went to my Square-Enix account and removed the extra character slot. However, since there is no billing cycle yet, the extra slot still shows up in my game client. Nevertheless I still only have one character on my Square-Enix account, so I will only be billed for the one character once subscription fees begin. Presumably the other character slot will go away then.