Sara Shiraishi is Shotaro's mother who was thought to have abandoned him when he was a newborn but that's not the case.  There is a deep secret that lies in her past and thus many people view her as a horrible human being. However, it is said that she was once a prostitute working on the streets to make ends meet, another rumor is said that she tried to use the Satanoka family name to become famous.

The truth is that she was once Yakunan Satanoka's mistress and once he found out she was pregnant he forced her to go into hiding after birthing their son.  

She is kind-hearted, loving and cares deeply for her son and daughter.  She doesn't enjoy watching from the sidelines of the abuse that Shotaro dealt with throughout childhood.  When she was able to help him she allowed him to move in with her when he was in college and did all she could to pay for his college tuition. She never told him the truth of who she really was and only told him she was "a friend of his mother".