Height 170 cm Yuiko is Riki's classmate who has a self-sufficient personality. She is sometimes seen carrying a replica of a katana. 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 (姉御, "elder sister") by Haruka. She is fond of things or people she considers to be cute, such as several of the female cast of characters. She gets high grades in school and is especially gifted in mathematics. She was born outside of Japan, but is still entirely Japanese. She was given the birth name of Elizabeth which would often be shortened to Lizbeth as a nickname but does not share this as she prefers to be referred as Kurugaya.

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Despite her flawless image, she has difficulty of grasping emotions and has faked any she shows. Simply, she just doesn't understand emotions. Due to her being really smart, she has been a subject to bullying and is even scorned by her teachers. Kurugaya also hates being called by her real name, Yuiko or nicknames (Yui-chan), as she only wants her future husband to call her something like that.