Mayumi works as a nurse in TPC, she joined the organization with the help of her older brother, and she sometimes has great sibling-type arguments with him. While in a flight returned to Japan to prepare for the Japanese Grand Prix and meet her, Takuma Aoki, her fiancé and a motorcycle racer, is killed by Gazort II in 15th episode. Takuma's soul returns to help Daigo and Shinjoh distract Gazort II in order to give them time enough to hide away from the monster. Meanwhile, Daigo transforms to Ultraman Tiga to fight and destroyed Gazort II. In the end, his soul gives Mayumi the necklace with her picture, which Takuma hold in his hands even the death is nearby, and tells Mayumi he always loves her before departing to afterlife.
In Ultraman Dyna, she was promoted to the rank of Head Nurse of the TPC.
- In the English dub, she is known as Marnie.