Numbuh 8a and Numbuh 8b were identical twin members of Sector V along with Numbuh 5, Numbuh 9 and Numbuh 11. They were struck by Chicken Pox during a battle with Teen Ninjas, as seen in Operation: M.A.U.R.I.C.E. They also appeared in Operation: T.R.E.A.T.Y. in a flashback of the moment Numbuh 1 joined the Kids Next Door. They are similar to Numbuh 44, as they are identical twins who share the same codename.
Despite fighting alongside and being commanded by Numbuh 1 during his early period within the KND, they were never actually mentioned by him or Abigail within the show, only appearing in flashbacks.