Ishiyama Descripition

As of "Lab Rat", Yumi is 15 years old, and therefore the oldest member in the group. As stated above, this has made her the mature person of the team, giving her the task of making sure the younger members, like Odd and Jeremie, don't get into trouble. She also has a crush on Ulrich, but they are constantly pestered by fanboys and fangirls of their own. Because of her age, she is a member of the ninth grade. Yumi also seems to have a brother-and-sister relationship with Jeremie, who seems to consider her third-in-command (with Aelita being second-in-command, of course). Yumi usually talks to Jeremie about her feelings about Sissi, Ulrich, and the others, as seen in Log Book.
Yumi likes wearing black, and all her clothes (and her hair) are that color. She is of Japanese descent, and even did a cultural report at school on her homeland in The Girl of the Dreams, bringing in some traditional samurai armor (she calls it "something that has been in my family for centuries"). She also sometimes integrates Japanese words into her speech, which only Ulrich and Odd can understand (once in Exploration and again in Vertigo). Yumi is the only student not boarding at Kadic. She lives with her parents and her younger brother, Hiroki, in a house not too far from Kadic, as she walks to and from the school.
Yumi's Lyoko attire is modeled after a Japanese geisha. She is the leader of the group in the virtual world, often jumping in to save the day at the last moments. It has been shown she is quite athletic in Lyoko, often leaping high into the "air" before throwing her Tessen Fans, her primary weapons. These tessen fans can also be used to absorb lasers from monsters such as Bloks, as shown in Mister Puck. In Lyoko, she can also use telekinesis to disable her foes, usually be dropping virtual rocks on them. In Season 1 she is easily exhausted by this mode of defense, however. In Mister Puck, she used her telekinesis in conjunction with her tessen, using it to steer an inaccurate fan mid-flight into a Blok. She may, on some occasions, lift other Lyoko Warriors with her telekinesis. One occasion, it was to lift Odd and prevent him from falling into the Digital Sea. In another---the episode Attack of the Zombies-- it was to lift Aelita to a tower that was made invisible.

Yumi's old real world outfit

In Double Take Yumi's outfit changes so that she wears a pink and purple body suit with flowered shoulder pads, she no longer has the geisha makeup on however she has two strange pill shaped objects above her eyebrows, her fans now appear and disappear at her will (as long as they are in her hands) rather than concealed behind the yellow bow on her back.
On Earth, it has been shown that Yumi is an excellent fighter. It seems she is skilled in various forms of oriental martial arts, including Pencak Silat, which she practices with Ulrich, as she fights her clone bravely in Image Problem, and is quite strong despite her physical build. She is also quite fast in the real world, and she holds the Kadic school record in the hundred metre sprint. She is also quite persuasive, as she often convinces teachers to let her go during a XANA attack.
Being mature and intelligent, Yumi usually isn't bothered by Sissi's rude comments, and has been known to understand Herb's plight and motives, as seen in The Robots. She doesn't have a strong opinion of the other students, although she has a good relationship with Jim (why she does is unclear), and is Jeremie's best friend.