Natasha Vasylchenko, codenamed Professor Um—derived from the Russian word for "mind" or "intellect"—serves as Zvezda's lead scientific and technological expert. Aged 15 with blonde hair and blue eyes, she holds Ukrainian nationality. Her childhood was marked by isolation; peers feared her robot-building pursuits. This loneliness ended abruptly when her parents took her underground to a "land of fairies," where she lost their grasp during transit, causing their disappearance. Natasha found herself transported to Japan's West Udogawa region, stranded within ancient Udogawan tunnels. There, she discovered or constructed the robot Roboko while encountering entities she called "fairies."

Rescued from the tunnels and these beings by Zvezda leader Kate Hoshimiya, Natasha and Roboko joined the organization. She now engineers Zvezda's technology, including transformation sequences and equipment, while primarily speaking in Hiroshima dialect. Typically clad in a white lab coat over black undergarments, Natasha exhibits a blunt personality, openly remarking on others' physical traits. She shares a close bond with Roboko, viewing the robot as her creation or companion, and maintains fierce loyalty to Kate due to her rescue. Within Zvezda's familial dynamic—highlighted by shared meals—she interacts with other members as part of the team, often appearing fatigued or sleepy from prolonged work sessions.