Seika Satanoka is Shotaro's second older sister and is deemed as a failure in her father's eyes.  Seika is soft-spoken, shy and timid. She doesn't enjoy disappointing her father nor does she speak up on her own behalf often. She has to protected by Saeko at times because she doesn't protect herself from being hurt or treated badly.  She was once married but divorced from her husband when she found out he was having an affair with another woman.  Her father then madae it a point to remind her everyday and that she "failed as a wife" and should try to do more to ensure that her next marriage doesn't fail.