Young girl Kaori who fell for unexplained thrombocytopenia showed a bizarre behavior seeking blood from that night. The cause was the space bacteria Dallie which has invaded her body was eating fibrinogen in the blood.
Dan infiltrates into Kaori's body by reducing his size and tries to get rid of Dallie, but he is forced to struggle in the "unknown world" of the human body.
This episode was influenced by the film Fantastic Voyage, released that same year.[2]
Fifteen-year-old Keiko Matsuzaka[3] played the guest character Kaori in one of her earliest acting roles. Matsuzaka would later become one of Japan's most celebrated actresses.
Screenwriter Shozo Uehara later recalled: " I specifically asked director Toshitsugu Suzuki to cast an exceptionally beautiful young actress for the role of Kaori. But when I saw the rough cut, I was disappointed to see a slightly plump, healthy-looking girl instead." That girl was Keiko Matsuzaka. I never imagined that this episode would mark her debut or that she would later become a national icon and renowned beauty. It was completely unexpected." [4][5]
In the episode, Kaori was portrayed as a university student, creating a contrast with Matsuzaka's actual age.
In the script, Kaori, who has lost her memory, reunites with Amagi and struggles to regain her memories. She vaguely remembers, "There was someone I longed to see every day. Being with that person made me happy."
The original script included a montage of Kaori and Amagi riding a carousel together, but her memories remained fragmented. In the final cut, this sequence was replaced with a simpler scene of the two characters gazing at each other.
The amusement park scenes used Track M51, Concerto for Flute and Piano, which was enhanced with a feedback effect to create an ethereal resonance.[6]
The original script had a miniaturized Ultraseven fly through Kaori’s nasal cavity, but he lost his balance and crashed after being struck by a sudden burst of airflow. This was changed in the final version so that Ultraseven is attacked by bubbles released from Kaori’s web-like tissue, which is controlled by Dallie.
Originally, the battle was scripted so that Ultraseven would kick Dallie off balance, slice it in half with his Eye Slugger, and finish it off with his Ultra Beam. Exhausted, Ultraseven staggers as the scene shifts to Kaori waking up in her hospital bed and finding a flower on her pillow. She lifts the flower to her nose to smell it, unaware that a weary Ultraseven slips unseen from its petals. This sequence was simplified in the final cut.
In this episode, art director Noriyoshi Ikeya completed the design of Dallie following Tohl Narita's abrupt departure from Tsuburaya Productions. According to a 2008 interview with Ikeya conducted by Yoichi Iwasa:[8]
Ikeya recalled that, even before Ultraseven, Narita often said he wanted to quit. Ikeya never took him seriously until he told Ikeya, "Next, it's up to you," packed his things, and left his desk completely cleared.
With Narita gone, Ikeya was the only one left who could design monsters, so he had to take over. At Tetsuo Kinjo's request, he designed a smaller creature called Dallie, basing it on fleas, lice, and mites. However, when he realized that Dallie had to enter a human body, he decided that those parasite-like designs were unsuitable.
Because the story involves Dallie invading Keiko Matsuzaka's body, Ikeya admitted that he always felt guilty when he saw her in films or on set.
