The Secret Hidden in the Bathroom (1) Meitantei Conan : Season 1 Episode 340

This episode reveals bits and pieces of Ai's family. Ai knows very little about her parents, and considers her mother a cold and mysterious woman, nicknamed Hell Angel by the Organization. Professor Agasa then brought Conan and her to the house of her father's old friend, who is also a professor. Later, after leaving the bathroom, that professor is murdered, leading Ai to believe the Black Organization is behind it.