Kenjirō Igarashi (五十嵐 健次郎 Igarashi Kenjirō) is a physicist who is Ryū Tenkūji's old research associate into the Eyecons and Gammas. He sought a way to save the Fukami siblings from the monolith but was unsuccessful because of Ryū's death at the hands of Adel as a result of protecting Takeru from a Gamma's attack 10 years in the past. This has left the professor traumatized and anti-social, particularly after he and Ryū discovered their former colleague Saionji has betrayed them for using the Fukami siblings as his guinea pigs for his experiments on the monolith to be able to enter the Gamma World, trapping the youngsters inside that world for 10 years, and now currently on the run from Saionji and Gammas. In the present day, Takeru tracks him down for help, which reignites his passion in the research to save the two, unaware that Makoto has freed himself and Kanon remains trapped in some fashion. He is targeted by the Green Dragon Blade Gamma because he still has the Benkei Eyecon, which he soon gives to Takeru. Many months later, Igarashi finally recovered from his trauma and returned to the Daitenkū-ji, happily seeing the Fukami siblings are alive well and manage to return to the human world. Before departing once more, he gives Akari his journal which contains translations to decipher the monolith's languages after acknowledging her courage as a scientist.
Kenjirō Igarashi is portrayed by Moro Morooka (モロ師岡).