Yumi Ishiyama is a highly valued member of the Lyoko Warriors. She is considered the maturest of the group, being a year older than the rest of them (beside William), and takes care of the younger members. She is both Ulrich's and William's romantic love interest, and Aelita Schaeffer's closest friend.

Personality and Characteristics 

In regard to Yumi's personality, her instant trademark is how she is shown to always prefer black clothes, basically the American goth look - with black sweater, black pants, and black boots. Her season 4 outfit is like her sports clothes consisting of a dark gray blouse and dark pants. She wears the same boots as in season 1-3. (This being seen in Cold Sweat where when an embarrassing childhood Halloween photo of her is seen, she is wearing big black boots in the picture.) She inspires coldness and distance at first glance. Rather abrupt and often of a sarcastic humor, she can seem particularly stiff and ironic. But this appearance exists only to hide her generous and sensitive inner nature, because behind this mask hides a being filled with warmth and with human qualities such as kindness, helpfulness, delicacy and sincerity. Yumi is shown to prefer getting acquainted and knowing people first before opening up to them, but once trust is established, she assumes a limitless fidelity towards the people whom she likes.

A fine observer, she is adept at understanding people and emotion. Good at sports, very smart (as seen by her responses to difficult situations), a hundred percent natural, she is the perfect opposite of Sissi and is very popular, although she seems oblivious to it. Also differing from girls her age, she rather prefers the company of boys, with the only girl she is shown to be close with is Aelita. Yumi is also a very applied pupil, who excels particularly in the literary subjects. Considered as having a great scholastic potential, she has the respect and trust of her professors which can be seen throughout the series.