Numbuh 3 (a.k.a. Kuki Sanban) is a character from Codename: Kids Next Door.
Billy & Mandy's Big Boogey Adventure
After Grim's title, rank and powers were removed, Numbuh 3 chooses to be the new Grim Reaper for a trial period of one month by The Boogeyman. This opportunity makes Numbuh 3 happy, excited to snatch souls of adults with the scythe.
Later, when Grim, Billy, Mandy, and Irwin fall asleep under the effects of somnífera cake, Numbuh 3 appears in the dream of Billy guise of a skull-like horse. Once the real Grim clarifies that the horse is not him, Numbuh 3 is revealed to all, mentioning that part Dreams Foundation for Stupid Boy. Thereafter, Numbuh 3 disappears having fulfilled her mission.
Finally, when Mandy required Judge Roy Spleen to give his post back to Grim by saving all of a future ruled by Boogey, Judge Roy apologizes to Numbuh 3 that she must withdraw the title as the new Grim Reaper and return it to Grim. Once done, Numbuh 3 swears revenge against Grim before disappearing. Judge Spleen acknowledges that she was a good reaper in her own way.
Thereafter, Numbuh 3 goes about being the Death of her own neighborhood in exchange for 25 cents for every soul, but nobody takes it seriously.
Billy & Mandy Moon the Moon
The Grim Adventures of the Kids Next Door
Numbuh 3 appears in Billy's house along with the rest of her team, the Sector V, to try to take Billy's pants from his father, Harold, with the scythe embedded in them. Seeing that did not work, decide with her friends bring Billy to KND Deep Sea Lab to try again.
During the trip, the Sector V gets a call from Numbuh 362, who informs them of a strange activity being conducted by The Delightful Children From Down the Lane, forcing the Sector V to deviate from the path. Arriving at the destination, and after the Delightful Reaper is created, and has his evil plan to assimilate everyone. Except for Numbuh 2, the rest of Sector V flees to the KND Moon Base, which inform Numbuh 362 about the Delightful Reaper while see Mandy posing as Numbuh 1, luring nearly everyone.
Once Mandy takes full control of the KND Commando, take Numbuh 3 and Numbuh 4 as her right hands, with whom part in the M.A.N.D.R.O.B.O.T. to face the Delightful Reaper. When Mandy left assimilated by the colossal creature, Numbuh 3 is assimilated at a time, although it is released along with the rest of assimilates as Numbuh 1 and Grim destroy the Delightful Reaper with help from Harold. Thereafter, Numbuh 3 maintains Mandy while she is detained in KND Moon Base with Numbuh 5. After Mandy escapes, she watches Harold drag Numbuh 1 while thinking he is Billy. The real Billy poses as Numbuh 1, causing everyone to start throwing things at him for being responsible for everything that happened.