Nyoronoru has written up another handy guide for Tatsunoko vs. Capcom, this time detailing one of the best defensive characters in the game, Saki Omokane.Saki is a keep away turtling character. Her entire job is to make sure you don't get in to combo her. She excels against the giants for this very reason. Combine her Hand Grenades, Beam Blast along with her Hyper, and it's very difficult for someone without a beam Hyper to lay on the damage.
Couple her with a good defensive partner assist, such as Chun-Li, and you've got an unapproachable character. Make sure you use her strengths to the fullest.