Kuki Sanban (codenamed Numbuh 3) is a happy-go-lucky, 10-year-old 4th-grader Japanese girl who is in charge of Diversionary Tactics and is the Medical Specialist of Sector V. She also takes care of the hamsters that power the treehouse. She is the youngest operative, and one of the two female members (alongside Numbuh 5) and the only Asian-American in her sector from the Cartoon Network show, Codename: Kids Next Door. She has a happy-go-lucky and pretty 10-year-old, fourth-grade Japanese girl who has a younger sister named Mushi Sanban and a future husband named Wallabee Beatles. As an adult, she becomes President of the Rainbow Monkey Corporation, and the first thing she did when she took over was tear down a Rainbow Monkey Potty training amusement park .
She is a happy-go-lucky, friendly girl who can be dimwitted or a comic relief sometimes. She is lovable and care-free just like Abigail Lincoln. She has displayed a like-like bond with Numbuh 4, though he is oblivious to his feelings for her. Despite her beauty, she is also corruptible, when she gets a hold of power, for example when she gained pyro-kinesis from her house's heated systems or when she got a hold of Santa's technology, she decided to take all the presents for herself.
She has black long hair, an over-sized green sweater, black tights and black and white shoes. Her hands rarely show when she is wearing a sweater, but when she wears different outfits, her hands show.
Numbuh 3 is described as the "Diversionary Tactics Expert", and is the nurse of medic lab and the hamsters' caretaker of Sector V. She has a very short attention span, but is long on charm, speaking in a slight Asian accent, and often alludes to her Japanese heritage. She is girly, optimistic, bubbly, dizzy-headed, clueless, kind, caring, patient, gentle, and arguably smarter than her teammate, Numbuh 4, upon whom she harbors a crush, as seen throughout the show, though it is less obvious. She loves Rainbow Monkeys, which she collects, fantasizes about, and has extensive knowledge about. Due to her great love for Rainbow Monkeys, she will often irrationally defend them, occasionally allowing her insanely aggressive side to show (generally accompanied by her face turning red, teeth and ears becoming pointed and eyes flaming, resembling an oni, a Japanese demon). Despite being generally good natured, she will occasionally have similar explosive tantrums when she is ignored or doesn't get what she wants. As shown when the macaroni Rainbow Monkey painting is accidentally shattered by Numbuh 13 in Operation: M.A.C.A.R.R.O.N.I., she has the ability to scream at a deafening volume. She is usually seen with a Rainbow Monkey doll, and her room in Sector V's Treehouse is filled with various stuffed animals and anything else colorful and fuzzy. A special ability of Numbuh 3's is that she can smell and sense Rainbow Monkeys with her nose and her heart as stated in Operation: R.A.I.N.B.O.W.S. and Operation: S.A.T.U.R.N.. She seems to also have a capability of speaking languages that would normally be dubbed gibberish or non-understandable, shown in Operation: D.I.A.P.E.R. and Operation: V.I.D.E.O.G.A.M.E. (Baby and Firefly, respectively). She is the pilot of Hippy-Hop, a giant mechanical rabbit that is equipped with a complete arsenal of weapons such as missiles and drills, with a running gag throughout the show that Hippy-Hop gets destroyed whenever it appears. Despite her attitude, Numbuh 3 shows her intelligence in a few episodes, such in Operation: H.O.L.I.D.A.Y., when it is apparent that she can pilot an airplane. In Operation: H.O.M.E., it was revealed that she had a Rainbow Monkey called My First Rainbow Monkey. Also, in Operation: L.I.C.E. she had a stuffed animal named Mr. Mopsey. Like Numbuh 5, Numbuh 3 also has a motherly side, as shown in Operation: C.A.M.P.. In this episode, she and Numbuh 2 take care of a skunk named Bradley, referring to the skunk as her baby. She often worries over Bradley and does whatever it takes to make sure that he is safe. Another example of her motherly side was shown in Operation: C.A.K.E.D.-T.H.R.E.E., when she helped Numbuh 1 take care of the baby chicks that had hatched.
- In the episode Operation H.O.T.S.T.U.F.F., Numbuh 3 serves as the main antagonist.
- The name Sanban means "Three" in Japanese.