Shizuna Endo is a member of the organization JUDA and the older twin sister of Izuna Endo. She serves as the co-pilot of the non-combat Machina Deceive, a machine specialized in electronic warfare, alongside her brother.

In terms of personality, Shizuna exhibits a brash and direct attitude, a stark contrast to her younger twin’s shy and reserved nature. She proves a supportive friend, willing to help others, such as when she and her brother taught the basics of JUDA to newcomers. One notable flaw is her strong Southern Japanese accent, a distinct Kansai dialect that emerges in her speech. This contrasts with her brother, who speaks standard Japanese, despite both having been raised in various places throughout Japan.

Physically, Shizuna is a 14-year-old girl of average height and build. She has brown hair cut into a neck-length bob with bangs swept to the right side of her face, and brown eyes. A distinctive white hair clip, gifted by Kouichi Hayase, is worn on the left side, initially serving to distinguish her from her nearly identical twin brother. Her typical outfit includes a black blazer over a light blue shirt, a loosely worn black tie, shorts, and light brown short fuzzy boots. As she ages, she reaches an average adult height and wears her longer hair in a hime-cut style.

The etymology of her name presents some ambiguity. Her surname, Endo, can mean "far." Possible meanings for her given name, Shizuna—which could be spelled in various ways such as 志寿奈, 玄奈, 静奈, 静七, or 寧南—include "Resolve," "Natural Life," "Nara," "Mysterious," "Occult," "Profound Nara," "Quiet Nara," or "Rather South." However, since both twins' names are not written in kanji, the precise meanings remain uncertain.

A notable aspect of her role involves the implication that she may never have been a true Factor for the Machina Deceive. This possibility arises from the circumstances of Izuna’s death and Deceive’s subsequent behavior, which included gaining self-awareness, trapping Izuna inside, and going on a rampage.