Kogorou Hashiratani is a supporting character in Brynhildr in the Darkness. He is the maternal uncle of the protagonist Ryouta Murakami and works as a scientist, having previously held a position as a doctor at a local university. Kogorou is a genius researcher with a strong background in biochemistry. A distinctive trait is his severe motion sickness, which affects him on any form of transportation, including bicycles and even pedestrian malls. Because of this condition, he declines all invitations that require travel and rarely leaves his campus. At the start of the story, Kogorou is skeptical of supernatural phenomena, but his perspective changes after he witnesses the magical abilities of the escaped witches, particularly Kana Tachibana's foresight and the events surrounding Nanami Tokou. He then agrees to assist Ryouta by analyzing the mysterious compound known as DR623G, or Death Suppressants, which the witches must take every thirty to thirty-five hours to survive. Kogorou succeeds in identifying the drug's composition and begins producing a substitute, effectively becoming the supplier for the witches in Ryouta's group. He also provides scientific insight into the witches' biology and the nature of their abilities. His role is primarily that of a behind-the-scenes ally who uses his intellect to solve critical problems and keep the witches alive. In terms of personal history, it is later revealed that he attended the same university as Chisato Ichijiku, another scientist who later becomes involved in the conflict, and he held a deep admiration for her. Kogorou's character develops from a reclusive, skeptical academic into a dedicated supporter who risks his safety to help the witches. Despite his eccentric limitations, he demonstrates strong commitment and even makes the long journey from Nagano to Tokyo on foot to deliver his aid. He survives the events of the series and continues his research into the witches' physiology and treatment. His notable abilities lie in his exceptional analytical skills and his capacity to reverse-engineer highly advanced technology, making him indispensable to Ryouta's efforts.