Touko Yotsuya is Mamoru Yotsuya's wife and mother to Miko and Kyousuke Yotsuya. She possesses chest-length jet black hair, typically tied in a low side ponytail secured by a light blue scrunchie that rests on her right shoulder. Her hairstyle includes bangs swept left and chest-length strands framing both sides of her face, paired with golden eyes. After meeting her husband, she established a family life and raised their two children. Her given name "Touko" merges the kanji 透 (transparent, permeate, filter, penetrate) and 子 (child), while the surname "Yotsuya" combines 四 (four) and 谷 (valley). She functions as a supporting character in the manga.