I was surprised when Gin turned against Aizen, stole the Hogyoku, after using the special ability of his Bankai, then Aizen regenerated and screwed him over... It was sad, because Gin was epic. Plus, I thought he was a bad guy for most of Bleach, then realised that he wasn't a bad guy at all... :(
Airi Yūnami from the Qualidea Code anime.
Maihime didn't realize the creature was her until she dealt the killing blow.
I wanted Ai to live and redeem herself.