Mushi Sanban (三番虫) is a five year old kindergartner, who is the younger sister of Kuki Sanban and daughter of Kani and Genki Sanban. Like her sister, Mushi is very childish and overly happy, but unlike her sister, beneath her outward personality she has a very sinister and conniving personality, despite her age. She also looks like the younger version of her sister, albeit with a different hairstyle and slightly paler skin.
Mushi constantly wears her hair in short pigtails held up by yellow pearl braids. She generally wears an over sized lavender jumper, black tights, yellow and pink socks and white Mary Jane's and she has a yellow backpack with a pink flower in the center.
She first appeared in Operation: S.P.A.C.E., in which her sister brings her along on a deep-space resupply mission, much to the chagrin of the other members of Sector V. When Cree makes a surprise attack on her sister while the other operatives are away, Mushi makes a heartfelt speech which convinces the two sisters to stop fighting, only for Abby to eject Cree into the garbage chute immediately afterward.
In Operation: K.A.S.T.L.E., she and her sister are captured by King Sandy and the Knights of the Round Towel in order for Sandy to force Kuki to marry him. During this encounter, Sandy inadvertently falls in love with Mushi and abandons his pursuit of Numbuh 3.
In Operation: C.L.U.E.S., the Sanban family comes to Numbuh 2's house for dinner. During the meal, a power outage occurs, and Numbuh 3's Rainbow Monkey disappears and is found inside the turkey case table with a fork in its back. Mushi is revealed to be the culprit of this "Rainbow Monkey murder"; she stole the Rainbow Monkey during the power outage, but, when she realized that it sighs when hugged, "killed" it in order to prevent this from being discovered.
In Operation: S.P.A.N.K.E.N.S.T.I.N.E., Mushi digs up the Rainbow Monkey doll from its burial site at Plush Meadows Stuffed Animal Cemetery and brought it back to life as a Spankenstine Monster using Count Spankulot's powers, and sent it after Numbuh 2 as revenge for the previous incident. However, she was grounded and spanked by Count Spankulot for this, but is then seen escaping from her room with King Sandy.
In Operation: I.N.T.E.R.V.I.E.W.S., Mushi and Sandy, working as a team, are among the numerous characters participating in the massive scavenger hunt for The Delightful Children's birthday cake. The two are seen stealing Professor XXXL's perfect snow-cone.
As of late, she appeared in Operation: B.O.U.N.C.E. of Cartoon Network Action Pack 39 along with King Sandy, in which they both tried and failed to seek revenge on Numbuh 2 for getting Mushi grounded for life.
- Mother: Genki Sanban
- Father: Kani Sanban
- Siblings: Kuki Sanban
- Future Brother-in-law: Joey Beetles
- Future Father-in-law: Sydney Beetles
- Future Mother-in-law: Mrs. Beetles
- Possibly future grandniece: Sally Sanban
- In Operation: I.N.T.E.R.V.I.E.W.S., Mushi makes a brief cameo appearance when Professor XXXL is making a snow cone and then she is seen stealing it along with King Sandy.
- Her name is Japanese for "bug" (虫) which reflects her annoying personality.