Jirou Enjouji is the younger brother of Daisaku Enjouji, one of the three primary pilots of the Albegas robots. He attends Aoba High School alongside his brother, sharing similar traits like a penchant for humorous and irreverent antics. Academically struggling, he is frequently labeled a "ne'er do well" by teachers, mirroring his brother's scholastic challenges.

When the Derinja civilization invades Earth, Jirou confronts the crisis with levity, cracking jokes amid the grave threat. He holds genuine affection for his older brother, though their bond often manifests as playful antagonism.

Jirou possesses a documented phobia of whales, rooted in an unspecified past traumatic incident. This fear serves as a recurring comedic device within the series. His primary narrative function is providing comic relief, frequently through exaggerated reactions or humorous misunderstandings.

His established traits remain consistent throughout the documented episodes, reinforcing his role as Daisaku's younger brother without substantial evolution or expanded background beyond this core function.