Keisuke Geiz, known as Kamen Rider Geiz, is a key character in the tokusatsu series 'Kamen Rider Zi-O.' He is a determined and principled warrior from the future, traveling back in time to prevent the rise of the tyrannical overlord Oma Zi-O. As Kamen Rider Geiz, he often finds himself conflicted between his mission and his developing friendship with the protagonist, Sougo Tokiwa (Kamen Rider Zi-O). Geiz's sense of justice and loyalty make him an essential ally and a complex rival throughout the series.