Wikipedia is totally my friend, as it sums this up quicker than I could -- But! Two classmates, Yuka and Asano. Yuka is effectively Youko's rival, and she's REALLY jealous when she finds out Youko is the chosen one -- she reads fantasy novels, see, and is therefore TOTALLY prepared for this whole adventure and is easily manipulated by King Kou to believe it was a mistake that Youko was chosen and that she can take her 'friend's' place.

And since I am running late now, I rip wholesale from Wiki re: Asano: "[He] is another one of Youko’s classmates and has known Youko since childhood. He is transported to the kingdom of Kou with Youko and Sugimoto, but goes missing after a battle between Yuka and Youko and is not seen by either of them for some time. Asano eventually becomes part of a group of Shusei and works for them as they traveled through the kingdoms. However, being in a completely alien country and lacking the ability to speak or understand the language, the strain has taken a toll on his sanity. Eventually, Asano questions the reason he was ever brought to Kou and seemingly can't find a reason for his life to go on. He dies at some point later in the anime. In the novels, Asano does not exist and Youko attends an all girls school."