An UTAUloid. Her voice comes from an amateur singer on NicoNico named "たぬＱ" (TANU Q). When drawn she is known to have dark hair that is in a ponytail.
She does not have an "official" outfit. Fans have been known to change her outfit for almost every video- although the underlining "shinobi" feel is a consistency with all of her appearances.
In some uploads and images, she is seen playing a violin. The genderbent version of Mako is (和音マコト Nagone Makoto).
(excerpts from Utau.wiki)