Touka is a member of the Evenkruga - a race/clan of bird-eared warriors who fight for honour and justice. She initially sided with a war lord who called Hakuoro his treacherous brother-in-law (who killed his family and innocents). It turned out that he was under an illusion spell which was dispelled after he was defeated, just moments before he got assassinated for silence. Touka offered her life (ritual suicide) as apology for the grave misunderstanding but Hakuoro wouldn't let her. Instead, she became one of his retainers.
She is a very serious girl who always has honour, duty and justice on her mind. However, she's actually a klutz (how that's possible when she's a master swordswoman... we do not ask) and a birdbrain - she can space out when she has a warm fuzzy feeling and pretty much melted apart when Gacatar (the small furry mascot animal) was introduced. Also, she has a doll from her childhood days which she is very emotionally attached to - has chased a wagon for several hours to get it back when she placed it there accidentally. In fact, she jumped off a cliff to grab it when it was finally tossed away - this event would create a whole legend of a demon in the form of a woman that chases you, with the only salvation being to toss a doll as a distraction.
Then there's the scenes from the original game, which understandably could not be shown in the anime. Those who have played it will know what I mean when I quote her line: "MOTHER! FATHER! TONIGHT, I SHALL BECOME A WOMAN!!!"