Komui is a tall man with dark eyes and long dark hair that curls at the end. He wears a pair of wire-frame, pentagonal glasses, a light blue turtleneck sweater, white pants and a white beret (which his subordinates claim they can sometimes hear noises coming from) along with his uniform, a white, Branch Chief coat. He also typically wears slippers, even at work, avoiding shoes because when he wears shoes his feet stink and Lenalee doesn't like it. After the European Branch moves to a new building, Komui's uniform changes; his turtleneck being replaced with a high-collared dress shirt and his white coat being replaced with a similar one, but with a cloth badge as well and several aigulettes rather than a metal Rose Cross.
Komui is initially shown as a very whimsical and goofy character, as well as being somewhat sadistic and occasionally borderline maniacal. He drinks coffee nonstop, favoring the Blue Mountain brand.He is also lazy and often tries to worm his way out of doing work by either running away from the office (Reever Wenhamm having to often track him down), talking on the phone non-stop even when the other side hangs up, and a multitude of other methods. During his naps, one of the only ways to wake him up is to say that Lenalee is getting married, which causes him to react angrily due to his "sister complex."
Komui, despite everything, does have a serious side, and it would seem at times his more whimsical side can be an act to support or distract his comrades given the situation. He feels guilty for putting the Exorcists and Finders in danger, and tries to help in anyway he can, such as making better uniforms to protect the Exorcists and making it difficult for Central to give Exorcists orders, forcing them to go through copious amounts of paperwork. He is also the one to repair damage done to the Innocence weapons, though the method seems very painful or at the very least traumatic. He has also shown a more solemn and ruthless side in the funeral for the Exorcists and Finders by refusing requests to bring General Yeegar's body back to his home and saying that the General's body must be cremated. Firm in his beliefs, Komui has shown a daring in refusing to follow Inspector Malcolm C. Lvellie's orders about keeping the Akuma Egg, and instead issues his own orders for the Egg's destruction.