Haran Banjo, born on Mars, is the sole survivor of his family. Self-aware cyborgs called Meganoids, rebelling against his scientist father Sōzō Haran, caused their destruction. At age 16, he escaped to Earth aboard a rocket containing the solar-powered super robot Daitarn 3, constructed from Martian metals. By 18, he resides in a luxurious Earth mansion, independently funding his operations while leading the fight against the Meganoids. Their leaders, Don Zauser and Koros, aim to forcibly convert humanity into cyborgs.

His core team includes his butler Garrison Tokida, former Interpol agent Reika Sanjō, combat specialist Beautiful "Beauty" Tachibana, and the orphan Toppo, whom he rescued during a Meganoid attack. Banjo's personality blends a calm, suave demeanor in non-combat situations—often displaying courteous, Casanova-like interactions—with intense ruthlessness in battle. This is especially true against opponents employing mind control, genocide, or justifications of "the greater good." Despite his hatred for Meganoids, he shows leniency to those demonstrating honor or capacity for love.

Key relationships include a past romantic involvement with Yukari Miyamura. This older woman later fell victim to Meganoid brainwashing, an event that profoundly impacted Banjo; his visible grief during her defeat is evident. His half-sister Ai Fujisaki and his father’s ex-wife Miwako Sawamoto—who became his legal guardian—further define his familial ties. He struggles to view Miwako maternally despite acknowledging her support.

In combat, he pilots Daitarn 3, employing signature attacks like the "Sun Attack" and vehicles such as the transforming car Mach Patrol. His battle quotes, including "The Sun Ring is within my grasp!" and "Sun! ATTACK!!," underscore his resolve. Spin-off novels collectively titled the Banjō Haran Series exist.