Hayashibara studied at a Catholic school, and at one point was bullied in fifth grade. She was an active club member and participated in the Badminton, Biology, Broadcasting, Drama and English clubs. She played the role of Alice in an English language production of Alice in Wonderland.
Despite qualifying as a nurse, she has never been employed in a nursing position.
On January 10, 2004, she announced on her radio show that she was pregnant with her first child. In June of the same year, she gave birth to a daughter.
Hayashibara later auditioned for Ranma ½ expecting to be cast as Akane Tendo, but was cast as the female half of Ranma Saotome instead.
In 1993 and 1995, Hayashibara was a guest at Anime America. At the 1995 event, she decided to give a speech in English after believing the translation at the 1993 event did not reflect what she had said.
In 1995, Hayashibara provided the voice of Rei Ayanami in Neon Genesis Evangelion, a role referred to as "innovative casting".