Her personality is pompous. Due to her popularity, she is held in highest hierarchy. Hence, she has no trouble making friends and also has little to no understanding towards people who have social troubles. Yumiko doesn't show interest, or mind anyone other than higher hierarchy of the class, which is noted by Hachiman by her attitude towards him. She holds herself in a very high esteem, and is not afraid to use her authority. It may be seen sometimes as if she forces her ideas onto the people whom she calls her friends. She doesn't like the idea of being opposed, turned down, or getting an answer not what she expects; this is shown during tennis court showdown, where Yumiko wanted to play tennis and doesn't heed to the words of Totuska, who got prior permission to use the court during lunch time.