is Riki's classmate who has a self-sufficient personality. She is sometimes seen carrying a replica of a katana called Muramasa. She is seen as an older sister to everyone despite being the same age of almost the entire cast, and is referred to as Anego by Haruka. She is fond of things or people she considers to be cute, such as several of the female cast of characters, especially Rin and Komari in particular. She is also seen as the most invincible member of the Little Busters, having defeated Masato, Kengo and Kyousuke, which traumatizes them. Rin is also afraid of her since Yuiko
is the only one who can contain and play around with her, much to Rin's dismay. Yuiko
gets high grades in school, especially in math, and is hated by her first year math teacher and several female students, who plan on bullying the Little Busters by first affixing nails and chewing gum to Riki's shoes. She was born outside of Japan, but is still entirely Japanese. When she was born, she was given the name Elizabeth which would often be shortened to Lizbeth as a nickname. Kengo was her classmate during her first year.