Tōko Yotsuya is the mother of Miko and Kyōsuke Yotsuya and the widow of Mamoru Yotsuya. During high school, she worked in prostitution. After entering a relationship with Mamoru, he disapproved of her occupation. She proposed that if he married her upon graduation, she would retire and become a housewife. Mamoru agreed, they married after graduation, and she left sex work as promised.

Tōko and Mamoru settled down and had two children. Following Mamoru's death, she became a widow and moved with Miko and Kyōsuke to Kurikami City. To support her family after her husband's passing, she resumed working as a prostitute.

Physically, Tōko is a striking woman with jet-black hair, typically styled in a low side ponytail resting on her right shoulder. She has bangs swept to the left and chest-length strands framing either side of her face, with golden eyes.

Her personality is characterized as kind and loving toward her children. She exhibits protective instincts, particularly concerning her daughter Miko, as seen when Kyōsuke searches for Miko due to concerns about changes in her behavior.