"Number Five" was a nickname given to a female officer serving aboard the USS Enterprise under Captain Christopher Pike, circa 2252. She was given this name as she was fifth in line to command the Enterprise after Pike. She did not object to this nickname, as it reminded her of how far she had to go toward her professional goals. (TOS short story: "Chaotic Response")

This character is clearly supposed to be a younger version of Number One, Pike's first officer from "The Menagerie".
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