Tieria IS a guy. So it can't be helped if he looks like a guy even if he can pass himself as a girl even without 'disguises'.
Too bad Feldt was underused as a character. I wish the producers just added some more episodes to make room to give some more meat to the characters and stories.
At least the series ending (not counting the upcoming movie) wasn't as bad as Gundam SEED Destiny's first ending. That was the worst ending I had ever seen in a anime.