Riyoko Ikeuchi is an adult female character characterized by brown eyes and black hair reaching her shoulders. She wears glasses and a necklace. Riyoko shares a personal relationship with Gorou Saruwatari, a main protagonist. During the first season, she interacts directly with Gorou as part of their established connection.

In the second season, Riyoko's involvement with Gorou transitions primarily to long-distance communication. This occurs via occasional impersonal transmissions while Gorou undertakes space missions for the International Space Agency. The available materials do not elaborate on Riyoko's background or personal history beyond her connection to Gorou. Her character development across the series consists solely of this shift from direct interaction to remote communication as the narrative progresses.