Jonah Matsuka carried the undetected Mu genetic factor, granting him psychic abilities. This allowed seamless integration into human society, where his powers were initially mistaken for merely unusual personal traits rather than Mu characteristics. He served as personal attendant to Keith Anyan aboard various spacecraft assignments, defined by steadfast loyalty. In this role, Jonah employed his psychic capabilities to shield Keith from hostile situations involving other Mu individuals.

He maintained a significant position as Keith's morality pet, demonstrating consistent devotion throughout their association. During their time at the education station E-1077, Jonah interacted with characters including Sam Houston and Seki Ray Shiroe. Shiroe investigated Keith's background through station computer systems, uncovering unsettling truths that ultimately contributed to Shiroe's demise.

Physically, Jonah possessed gray curly ear-length hair and distinctive yellow eyes. His narrative concluded when he intervened in an assassination attempt targeting Keith Anyan by Tony, sacrificing his life to protect Keith and suffering a fatal wound. Jonah's death profoundly impacted Keith, who preserved Jonah's blood within personal earrings as a memorial.

Across different media adaptations, the character's surname occasionally appears as "Makka" in translations due to interpretation discrepancies of the Japanese source materials.