|Played by|| Takashi Taniguchi (Voice Only: 21, 23, 26),|
Unlike previous incarnations of the character Dr. Kisaragi, who were benevolent scientists caught up in the machinations of Panther Claw leading to their death. Koshiro is depicted as a cold individual who is obsessed with his work and cares little of the consequences of his actions, save for the death of his daughter. His death is a result of his own selfishness rather than at the hands of Panther Claw. His actions of murder and kidnapping to regain his daughter make him much more of an evil mad scientist incarnation of the character, despite his sympathetic intentions. However rather than just discard them like garbage, Dr. Kisaragi provided the girls with flawed Honey System's the means for good lives for the remaining time they had left.
In the special DVD exclusive episode of the series, Dr. Kisaragi's backstory is given. Koshiro was a scientist who was obsessed with completing his work on the Airborne Element Fixing Device. Because of this, his wife divorced him and left their daughter in his care after she was born. He showed little affection for his daughter and cared only about completing his work. While he was working on the device, his daughter tried to give him a letter of encouragement on a playing card only to be disintegrated by the device, much to Dr. Kisaragi's horror. However, he at first coldly considered it as the first experimental data on the project, stating in his diary that his device could destroy humans. As time went on however, he began feeling grief over the loss of his daughter and emotions of denial and obsession about bringing her back, going so far as to say she merely "disappeared" in his diary.
He then began experiments on unwilling test subjects to bring his daughter back, starting with Miki Saotome, killing her parents using the device and abducting her. He brainwashed her and reformatted her memory to be exactly like Honey, then used her as a test subject for his "Honey System" a smaller version of his device. He later considers the first experiment a failure, as Miki's memories began to resurface and her Honey System began to go out of control. He then planned to discard her by setting her up with Masayuki Nemoto.
He sought a new test subject, a terminally ill girl named Yuki Kenmochi, he killed her parents using the device and abducted her from the hospital. He reformatted her memory entirely and added an artificial organ to better regulate the Honey System. This in turn cured Yuki of her illness. Despite this, the system was still flawed and caused random objects to appear out of nowhere. He then sent Yuki away to a family composed of a pair of androids he created to live her remaining days until her body gave out from the Honey System.
Frustrated with the failures of both experiments, Dr. Kisaragi decided to build an android who would be the perfect representation of his daughter. A being who would embody unconditional love for humanity as well as himself. However as he constructs Honey, Miki learns the truth about her past as well as Dr. Kisaragi's plan on discarding her and that he killed her real parents. Miki confronts him and in her rage kills him by stabbing him in the gut with the Boomerang Bleu. Honey wakes up for the first time, searching for her father, only to find his corpse lying on the ground. Afterwards, Honey buried him in the forest where his flesh rotted until he was nothing but bones.
His remains were found about a year later by forest workers who turned them over to the police which Panther Claw tried to steal. The three flash girls however teamed up to get them back and after a long fight managed to recover them. While Miki was ready to throw the container the bones were in into the ocean, Yuki tried to attack her. Honey broke up the fight, and revealed that she was the one who buried him the first time. Dr. Kisaragi was later given a proper burial by his creations but with different intentions.
Seiji Hayami would later find Dr. Kisaragi's diary as well as his research before burning them to make sure they never got into the wrong hands.
Dr. Kisaragi is an accomplished scientist in both physics and robotics, although which institute he worked for is unknown as well as his funding. He is able to create the powerful Honey System which can use the elementary particles in the environment to create objects and perform various other tasks. In other fields, Dr. Kisaragi made two girls into functioning cyborgs as well as the human-like android Honey.
- Dr. Koshiro Kisaragi's motivations can be compared to that of Sou Fueki from Kamen Rider Wizard. As both men lost their daughters and would willingly cause death and destruction to resurrect them.