I don't know how to write the introduction. It's probably just a story about a villain who suddenly wakes up.
The heroine has no memory of fetal transfusion. She is a professional lawyer and once took over the commission of the shooting/murder case of the Wayne couple.
Twenty years later, he discovered that his mother was responsible for the serial murders. After an inner struggle, he defended his innocence and won the case. Afterwards, the relationship became estranged. A year later, the mother left evidence of the crime and committed suicide. There was a suicide note on the table saying, "I hope my coolest girl can stand in court and expose the crime."
The heroine suffered a mental breakdown, but improved under Harley's treatment, and she remained a normal person on the surface.
After Harley became Harley Quinn, her condition worsened. Harley's [psychiatrist version] voice appeared in her ears, and she collapsed completely.
So the villain who beat up our teammates appeared, dated Harley Quinn, and performed "I'm not here to tear you apart, I'm here to join you" to the Joker [he failed to assassinate the Joker many times, so he joined].
After recovering his [past life] memory, he felt that Harley Quinn was too angry with him and broke up with her.
Harley chased his wife at the crematorium [she had other relationships before she got her back].
Purpose: My dear friends, clear mines on your own