Linda is the younger sister of Peter Johansen (Hoihensu in Japanese sources). Both siblings share a mixed heritage, born to an Earth scientist father and a mother from Planet Pineron. This Pineron ancestry grants Linda a distinctive star-shaped birthmark on her forehead, a trait marking individuals of Pineron descent and making them targets during the Earth-Pineron conflict.

Following their father's mysterious death after torture for war non-cooperation and their mother's imprisonment on espionage charges in a concentration camp, Linda and Peter become orphans. They are placed under the guardianship of Professor Socraton (Socrates), a longtime friend of their father.

Linda's role emerges from her vulnerability as a child marked by her Pineron heritage. Her capture by Earth authorities during the conflict becomes a critical catalyst, escalating the stakes and directly motivating her brother Peter's transformation into the masked superhero Yuusei Kamen to rescue her and fight injustice.