Shortly after fleeing from her captors after arriving in Kou, Youko Nakajima sneaks into Takki's house and attempts to rob her. Takki takes pity on Youko, explaining a number of general things about the Twelve Kingdoms to Youko. Seeing as Youko is stranded, Takki offers Youko in Kasai, where her mother works. Because of Takki's seeming kindness, Youko accepts. However, upon arriving in Kasai, Youko overhears that Takki's true intention is to sell Youko to Takki's mother, the mistress of a brothel, as a slave. Realizing that Takki is not to be trusted, Youko flees.
In the anime, Takki's role is largely the same and she first appears in the third episode. Like in the novel, Youko attempts to rob Takki's house, although she is accompanied by her classmates Yuka Sugimoto and Ikuya Asano. Takki takes pity on all three of them, offering clothing, food, and shelter, and then offers the two girls a job in town, though once again, her intention is to sell the two girls as slaves.

(Source: 12kingdoms.wikia)