Professor Hideo Midorikawa (縁川秀雄-教授, Midorikawa Hideo-kyouju) was a university professor and notable researcher of computer programming and engineering. He was an acquaintance of Takahiro Kurosaki, who referred Soichiro Kurebayashi to Midorikawa as a research assistant. Soichiro, whose parents recently died and now needed to support himself and his younger sister, felt indebted to Midorikawa for the support he provided. Midorikawa is also known for writing a number of books on programming and coding, which Kiyoshi Hasegawa has read.
Professor Midorikawa was involved in the research of encryption of programming codes such as "Jack," which had the potential to become a threat to national security. It was implied that he was aligned with Takahiro Kurosaki and the politically moderate faction monitoring and attempting to regulate "Jack"'s development. However, at an unknown point in time, Midorikawa betrayed Kurosaki and accused him of being a spy for releasing information to foreign governments. Kurosaki mysteriously died some time later.
After Takahiro Kurosaki's death, Midorikawa became involved with the research and decryption of the virus code "Jack o'Frost," a programming code developed by Takahiro's son, Tasuku, who had become a hacker in order to expose the truth behind his father's betrayal and death. When the previous factions involved with "Jack"'s development emerged and attempted to obtain "Jack o'Frost" to destroy the original "Jack" code, Midorikawa approached Soichiro and Kazumasa Andou for help in order to solve "Jack o'Frost". Soichiro refused in accordance to previous agreement that he would not involve himself in Midorikawa's projects, but agreed to hold onto a letter for Tasuku should anything happen to Midorikawa. Shortly afterward, Tasuku was coerced into reproducing "Jack o'Frost" and Midorikawa was murdered by an unknown assailant. In letter disclosing Midorikawa's last words to Tasuku, he apologizes but does not reveal the motives behind betraying Takahiro, admitting he does not feel he has the right to absolve himself.
Regardless of Midorikawa's motives for betraying Takahiro, he remains respected by Soichiro and Tasuku Kurosaki, who both feel that Midorikawa has done a great deal for them.