|Image gallery for Yūko Nishi|
Yūko is a beautiful girl with butt-length black hair that has bangs swept to the right side while she has waist-length hair strands hanging in the front, purple eyes and a tall and endowed figure, which Tōru Ichii envies, that's why Yūko is often the subject of Tōru and Nagisa Tennōji's teasing. She is often questioned if she is a model, because of her slender and tall figure.
Yūko is a scaredy-cat as she gets scared very easily, but she says if she closes her eyes, she won't get scared, but Tōru Ichii, who enjoys teasing her, prevents Yūko from closing her eyes by staring at her. Nagisa Tennōji also teased her when they went to the school at night, where Yūko got her fright of her life. When she gets uncomfortable, she clings to somebody (specifically Nagi).
She has a knack for cute stuff especially teddy bears, her room was shown that almost all in her room was teddy bear filled, even some posters were there.
She is a very kind, caring, and thoughtful person, because even though Tōru often teases and scares her, she is still kind to her, such as when she insists they celebrate for her birthday even though Tōru says she doesn't need a celebration.
She is also quite a worrywart, shown when she immediately panicked when she mistook the first year's fooling around as a help signal, thinking it was a fire, as well as worrying about Run Momoki falling from her chair when she slept during class.