*She is of Irish ethnicity. She hates boys, believing that they are universally inferior, and frequently allows her feelings to influence her actions and decisions against rational logic. Numbuh 86 was introduced in Operation: F.U.G.I.T.I.V.E. and since then has been a major recurring and supporting character throughout the run of Codename: Kids Next Door.

Fanny is almost always seen wearing a makeshift Samurai-style helmet which conceals her red, wavy, and frizzy hair, a green sweater with orange and yellow shaped circles on it with (which are part of her uniform as a KND operative and are taken off when she is inactive), an orange skirt and brown boots. In Operation: F.O.R.G.E.T. she is shown to have green eyes. She carries a yellow holster which contains her 2x4 Technology device, called a M.U.S.K.E.T..

In Operation: S.L.U.M.B.E.R. and Operation: D.A.D.D.Y. she is seen with a yellow Rainbow Monkey night gown and a pair of purple Rainbow Monkey slippers. As a child in Operation: M.A.U.R.I.C.E., she wore a nurse's hat, carried a first aid kit on her hip, and had red cross stickers on her shoulders instead of orange circles. Her hair was worn in ponytails with green hair bands.

In Operation: H.O.L.I.D.A.Y. she was wearing a green tankini top and white with green lace flip-flops. She also had on a yellow and orange beach sarong in a checkerboard pattern without her Samurai-style helmet on.

Numbuh 86 speaks with a thick Irish accent and has a loud voice, especially when she yells which she does often especially for someone so rude. She is rude, ill-tempered, bossy, stubborn, hypocritical and mean, but is strongly loyal to the Kids Next Door. As mentioned above, she has a strong distaste in boys, most notably shown during her first appearance in Operation: F.U.G.I.T.I.V.E., where she essentially takes Numbuh 1, Numbuh 2, and Numbuh 4 out of a mission simply for being boys and instead readily listens to Numbuh 5 and Numbuh 3.

She does seem to have a soft side, however. In Operation: M.A.U.R.I.C.E., she cries (along with everyone else) when the beloved male operative Maurice is decommissioned. In Operation: C.A.K.E.D.-F.I.V.E., she ends up falling for Numbuh 19th Century, who is inadvertently sexist, and is found kissing him when they are rescued from their cell. In Operation: E.N.D., she tells Numbuh 4 that she always thought he was cute as she was about to decommission him. In Operation: S.L.U.M.B.E.R., it's revealed that Numbuh 86 is secretly a fanatic of Rainbow Monkeys and that she has a bedroom full of them. She does not want any boys to discover this and threatens "Numbuh Four Thirtyteen Seven" not to tell anyone, saying "If you tell any of the stupid boys I'll kill ya." Indicating that even though she's annoyed with them she cares what they think of her.*