Eriko Aizawa is a main character in the manga Jiraishin she is the main character Kyoya Ida's second partner after the death of Hachimaki and when they met she had a boyfriend named Kouhei Asada, has an older sister and her parents are still alive.
Eriko was inspired to be a police officer in an incident 7 years before her introduction in the manga, her older sisters baby daughter died in a tragic accident in which the baby was fatally bumped on the head and died of a brain hemorrhage.
But then the police became suspicious when they found out about an expensive life insurance policy and also the circumstnaces of Eriko's brother in law whose business was not doing well at the time added to their suspicions.
It was 3 months before the police finally concluded their investigation and it severely affected her sister and brother in laws brother marriage, especially over the insurance policy plus the Aizawa family got something of a bad reputation.
Eriko angrily confronted the Detective who investigated and yelled at him but the Detective calmly explained:
"No matter how much you insult us we'll still suspect anyone if there's the slightest chance it was murder. If it really was murder who else can lay the dead to rest."
Upon hearing the Detective explanation Eriko realized how much she had wronged him and chose to become a police officer.
Upon making Detective she was partnered with Detective Kyoya Ida.