Keiko Arima

is the wife of Kodai Arima and the biological mother of Takuya Arima who is dead prior to the series' beginning.

Trivia

 * The name Keiko means "celebrate" (慶), "respect" (敬), "open, begin" (啓) or "favor, benefit" (恵) (kei) and "child" (子) (ko).
 * Keiko's surname Arima means "exist" (有) (ari) and "horse" (馬) (ma).