Gengorō Ueki (植木 源五郎, Ueki Gengorō) is Kōsuke Ueki's adoptive father. He is a writer and likes anything weird or unusual. Rather than being shocked or scared at peculiar things, he shouts in excitement, especially when he saw Tenko for the first time ever. He gets crazy, over Tenko, even squeezing and stretching his face. He also enjoys sports.