Megumi was a medical student who studied in the same university as Black Jack. She was also in love with Black Jack, but never told him this until the day of her operation, who in turn confessed he was in love with her also. Her operation was a success, but the removal of her female parts forced Megumi to change her name and start living her life out as Kei Kisaragi.
Not much of her personality was shown but she appeared to be fearful and easily frightened. However, she is also observant and despite having a bad first impression of Doctor Black Jack she quickly understood he was a caring person who watched over her. However, she was too shy to reveal her feelings to him and her feelings only grew stronger until the day she had ovarian cancer and required surgery.
Megumi studied in the same university and was trained in the same medical department with Black Jack. At first, she was afraid of him due to his appearance. When she worked late and it is raining, there is always an umbrella waiting for her which is left by Black Jack secretly. Besides that, he also follows Megumi secretly as well to ensure that she is safe until she reaches home. One night, she was attacked by a gang of punks while walking back home. However, she is saved by Black Jack. Since that day, she started to fell in love with him but never confessed her love to him.
One day, she was struck with uterine cancer and Black Jack examine her everyday. Having no choice since the cancer is in a bad stage, Black Jack directly told her that she would no longer be a woman as he had to remove her reproductive organs. Before the surgery began, Black Jack confessed his love to Megumi and gave each other a final kiss. The operation was a success but Megumi is now no longer a woman, now living her life out as Kei Kisaragi, her "brother".