Orphaned early on Sandy Planet (later revealed as ancient Geminar), Photon Earth was raised by the tribal chief's family. He formed deep bonds with the chief's granddaughters, especially the eldest who served as his primary caregiver until her marriage and departure. His childhood involved frequent responsibility for managing the headstrong younger granddaughter, Aun Freya. Photon uniquely ignored and countered her time-freezing abilities due to an innate resistance to various energies, including her stasis fields. This stemmed from being a natural source of "un-Aho" or anti-Aho energy, allowing him to physically disrupt her powers, often by striking her head with his black crystal quarterstaff.

Photon possesses immense superhuman strength and exceptional durability, enabling feats like shattering crystalline barriers bare-handed and withstanding direct Aho energy blasts unharmed. These physical capabilities make him a formidable combatant, though he typically employs his strength defensively or reactively. Despite this power, he exhibits a simple-minded, gentle, and trusting nature. He communicates minimally through grunts or basic phrases and displays childlike behaviors like excessive drooling at the sight of food. His thought processes prioritize promises of protection and immediate needs over complex planning or social nuances.

His pivotal development began discovering a crashed starship while searching for Aun after she stole a sacred artifact (a marker). Inside, he encountered Keyne Aqua, a rebel pilot in suspended animation. Irritated by Aun's prank of writing "baka" (idiot) on his forehead, Photon vented by scribbling the same word on Keyne's. Unbeknownst to him, this triggered an interstellar marriage custom, legally binding them. He perceived Keyne primarily as a reminder of his former guardian due to their similar appearance. This accidental marriage propelled him into galactic conflict, teaming with Keyne to evade imperial commander Papacharino Nanadan, who sought "Aho energy" secrets.

Photon remained largely static in personality, retaining his simplicity and loyalty throughout subsequent events. He inadvertently attracted romantic attention from Keyne, Princess Lashara Moon, and Papacharino's former henchwoman Pochi #1, yet remained oblivious to their affections. His protective instincts extended to all companions, notably fulfilling his oath to safeguard Aun despite her volatile behavior. In the concluding episodes, he inadvertently formalized marriages with Keyne, Aun, and Lashara by repeating the forehead-marking custom, never comprehending the implications.

Lore connects him as a distant ancestor of Empress Lashara Moon from the Geminar lineage, evidenced by shared surnames and creator-confirmed canonical links between Sandy Planet's future and the world of *Tenchi Muyo! War on Geminar*. Concepts like Aho energy and Koros (small hamster-like creatures) persist through this lineage, though Photon himself remained unaware of this legacy.