Cynthia Dolphin (シンシア・ドルフィン, Shinshia Dorufin), named Iruka Dolphin (イルーカ・ドルフィン Iruka Dorufin) in the original manga serialization and some reprints (see "Notes"), is a minor character that appeared in the November 1965 side-story "The Aurora Strategy". She is the daughter of Dr. Dolphin, one of Dr. Gilmore's colleagues and a British scientist that had developed the Mad Machine.
Cynthia is a teenage girl, presumably around 009's age or a little younger. At the beginning of the story, she is seen wearing a blouse and jumper skirt. She has brown hair that she wears tied back into a ponytail, and wears a yellow bandanna tied around her head.
Later on in the story, she wears a yellow coat with gold buttons (similar to the ones on the 00 uniforms) and white fur trim, as well as yellow leggings and matching fur-trimmed boots.
Cynthia is introduced as a kind, yet naive young girl who is at first very appreciative of 009's help in helping her find her father. However, she is soon revealed to have a hate of machinery, due to her father neglecting her to work on his experiments. This has to lead her to hate all machines and technology and find them frightening, with her going as far as to confess to even hating motor vehicles.
By the end of the chapter, Cynthia appears to still hate machines, however, the final panels with her glance and sorrow may be left up for interpretation and to suggest that she's become conflicted of what to really believe, along with the fact that she may fear 009 now since he represents a machine.
Cynthia was alerted to her father's kidnapping by the Neo-Nazis by Dr. Gilmore and the 00 team, and offered a place at Dr. Kozumi's for safety purposes. However, while 009 was driving her to go get her belongings, she confessed that she had come to loathe her father due to him leaving her all alone to work on his machines. The two were then ambushed by Neo-Nazis, and 009 had to reluctantly let Cynthia be captured in order to find their base.
The 00 cyborgs stowed away on the plane to Antarctica to track the Neo-Nazis, but soon found that Cynthia was to be tortured in order to make her father confess how to activate the Mad Machine.
After Cynthia and her father were rescued, the Mad Machine wound up activated, causing pain and instability in the cyborgs and revealing their secret to the two. While 004 managed to destroy the machine, Dr. Dolphin soon confessed that he had developed it to avenge his wife, who had been maimed by a Nazi V-1 strike in WWII and who had committed suicide after Cynthia's birth, having become traumatized by her disfigurement.
Cynthia was overjoyed to realize that her father hated machines as well, and to learn the reason of why he had abandoned her for so long. But she soon realized that she'd expressed her hate in earshot of 009. After the other cyborgs noticed her fearful and conflicted expression and her turning away from 009 in tears, the team parted ways with Cynthia to return to Japan.
- The story was heavily restructured for reprints, with a flashback being added to illustrate Dr. Dolphin's past (it had previously only been available through his text-only monologue). Due to this, the linework on the panels on the last few pages do not match up with each other. The dialogue bubble of Cynthia stating "Machines..." and trailing off (adapted as a more upfront "Machines are evil..." in the Tokyopop translation), and the panel of her turning back towards her father in fear, were also newly-added, adding more of a bittersweet significance to her and Joe glancing at each other.
- The original printing also had the team operating out of a base in England, and Dr. Dolphin and Cynthia living at a house on "Holmes Street". As Shotaro Ishinomori opted to place this story between the "Assassin" and "Wandering" arcs for whatever reasons, the story was rewritten to have Dr. Dolphin and Cynthia living in Yokohama and Cynthia attending a religious boarding school in Tokyo. Despite this, many panels were not redrawn or altered, and the setting still appears very British (the place identified as Dr. Kozumi's house also looks nothing like the villa seen in the other chapters).
- Despite Ishinomori himself renaming the character from "Iruka" to "Cynthia" in the first reprint in 1966 and the name sticking through the next few decades, some materials published through 1998-2003 reverted her name. These include the Shotaro World and MF Comics editions of the manga, along with Junichi Fukuda's Shotaro Ishinomori Character Guide. As a result of sourcing off the MF Comics printing, the Tokyopop translation of the manga may also continue the impression that "Cynthia" was only a change that came as recent as the 2001 anime adaptation. The most recent re-releases of the manga through the Complete Works collection have corrected her name back to "Cynthia", with the Italian and French translations sourcing from that edition.