|Relations||Suguru Koshigaya (son)|
Komari Koshigaya (eldest daughter)
Natsumi Koshigaya (youngest daughter)
Yukiko is a pale-skinned older woman with dark black hair that has bangs swept to the left, grey eyes, she is usually shown with and angered expression on her face and she is mainly shown in a tee-shirt and slacks.
Yukiko is known to be particularly strict, especially towards Natsumi Koshigaya. She tends to yell at Natsumi a lot because she tends to disobey her... a lot. Yukiko is a very disciplinary mother and wants her children to obey her. It would seem that her parents may have been very disciplinary towards her seeing as she is towards her children especially when they lie. She praises the other children such as Renge Miyauchi and Hotaru Ichijō because she wishes her children would follow their example.
- The name Yukiko means "snow" (雪) (yuki) and "child" (子) (ko).
- Alternatively, it can also mean "reason, cause" (由) (yu), "joy" (喜) or "valuable" (貴) (ki) and "child" (子) (ko).