Kuki Sanban a.k.a. Numbuh 3 is a happy-go-lucky, 10-year-old 5th-grader Japanese girl who is in charge of Diversionary Tactics and is the Medical Specialist of Sector V. She is the youngest operative, and one of the two female members (alongside Numbuh 5) in her sector. As an adult, she becomes President of the Rainbow Monkey Corporation.
Numbuh 3's usual outfit is an over-sized green shirt, black leggings, green socks, and black and white Converse. She has long black hair with bangs. Her eyes are very thin, almost appearing closed most of the time, although she does open them wider on occasion. She has more alternative costumes than any other characters in the 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.
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.