Yūko Okonogi (小此木 優子: Okonogi Yūko) is a character in the series Dennō Coil; she is nicknamed Yasako, which is another reading of 優子 meaning "gentle girl". She is an elementary school student with brown hair. With her sister Kyōko and her two parents, Yasako moves to the city of Daikoku to live with her grandmother, Megabaa. Yasako is a sweet and passive girl who follows the lead of Fumie, who eventually initiates her into Megabaa's Coil Cyber Detective Agency as its eighth member. Yasako has been to the city of Daikoku seven years ago for her grandfather's funeral. A pair of dennō eyeglasses and the virtual pet Densuke were left to her as a memento. During her time in Daikoku, she coincidentally wandered into the Coil Domain where she befriended a young boy with the codename 4423. After Yasako returns to live in Daikoku, her hazy memories of that enigmatic friendship gradually return to haunt her. Her father Ichirō works at a Dennou technology company, Megamass, which deploys Searchmaton in Daikoku. Her birthdate is October 12 2015.

She is voiced in the Japanese dub by Fumiko Orikasa.