- "So there's some mysterious link between that game and the Epitaph of Twilight. Interesting."
- — Yuuko Asaoka —
Yuuko is a childhood friend of her school's tennis club captain, Koura. She is also a friend of Akira Hayami. Initially, her role is merely that of a friendly upperclassman. During .hack//Another Birth MUTATION, she gives Akira information about the Epitaph of Twilight - information that BlackRose would later use to solve Sheraton's riddle. As one of the juniors that are actually friendly to Akira, she was harassed by the same three girls that bullied Akira earlier. Despite this, she doesn't show any signs of being affected by the attacks and remains a good friend of Akira. She later helps Hagiya's attempts to get Akira to go out with him.
Yuuko is also knowledgeable about the Epitaph of Twilight and helps Akira make some sense out of the fragments she collected in The World. She invites Hagiya, who also knows about the Epitaph, to the same meeting after he sees her Epitaph printouts. It is Asaoka who comes up with the theory that Morganna was created to give birth to Aura in Emma's place and turned against her programming once she realized she would cease to exist once Aura was complete.
Asaoka graduates from high school at the end of the last novel.
- Yuuko's interest in the Epitaph of Twilight began when she saw it quoted as an epigraph in a doujinshi.