Sonoko is a fair-skinned young woman with chin-length dark blue hair and light blue eyes.
She is usually seen wearing a black work blazer, a white button-up shirt, and a black knee length pencil skirt.
Sonoko is a calm, collected and hardworking young woman who is also very mature but she acts childish at times.
Sonoko is Utaha's editor and they both seem to trust each other as Utaha has never lied to her about her books. However, they sometimes can argue about some small things. Sonoko calls Utaha Shi-chan" to tease her.
- The name Sonoko means "garden" (苑) (sono) and "child" (子) (ko).
- Sonoko's surname Machida means "Town" (町) (machi) and "Rice Patty" (田) (da).