Sa-chan (さっちゃん, Sacchan) is a girl who attended the same kindergarten as Mamura.
Sa-chan has shoulder-length dark-colored hair with one bobby pin holding back her fringe, as well as dark-colored eyes. She is seen wearing a dress in Mamura's flashback.
In Mamura's flashback, she is seen to be friendly towards Mamura, as can be seen when she and her friends invite him to play house together. She is also shown to be sensitive, as she suddenly cries when Mamura rejects them bluntly, although that is not unusual considering her age.
In Mamura's flashback, Sa-chan calls out to Mamura and calls him "Daiki-kun." She and her friend proceed to invite him to play house with her. However, Mamura bluntly says, "No way," which causes her to cry because of how mean he was being.
She proceeds to say to Mamura that what he just said had been very mean. Sa-chan's friend also complained to their teacher that Mamura made Sa-chan cry. The teacher then went up to them and scolded Mamura, saying that what he did was "no good." Despite this, Mamura did not think he had done anything wrong, as what he had told her about playing house being boring was true. He also believed that Sa-chan's cries were faked, as no tears had been coming from her eyes.
- The way Sa-chan's name is spelled in Japanese, "Sacchan," is a commonly used cutesy abbreviation for a girl's first name when combined "-chan." As such, it is most likely that Sa-chan's name is not just "Sa," but instead a longer name beginning with "Sa."
- Like Mamura's older brother Daishi, as well as Mamura's mother, she has only been seen in the final chapter—day.78—within Mamura's flashbacks.
- Sa-chan is one of the few characters without an animal in their name.
Yasuo Minamoto - Tanaka - Yada - Ririko Nekota - Yuyuka's father - Yuyuka's mother
Suzume's father - Daishi Mamura - Mamura's mother - Sa-chan - Samejima - Odawara