Ruriko Midorikawa is a key character in the Kamen Rider series, especially significant in the original 1971 show. She is the daughter of Professor Midorikawa, a scientist who is involved in the creation of the Kamen Rider cyborg. After her father's death at the hands of the evil organization Shocker, Ruriko becomes an ally of Takeshi Hongo, the first Kamen Rider. Her role is pivotal as she assists the Kamen Rider in his fight against Shocker and provides emotional support and motivation, often acting as a moral compass in the series.