Sunred, also known as Astro Fighter Sunred, is a Japanese sentai-type superhero and main protagonist of the series, approximately 27 years old. Despite his role as a hero, he maintains an athletic, stuntman-like build though he leads an unhealthy lifestyle involving smoking, drinking, and little exercise outside of combat.

He constantly wears a red helmet featuring a yellow sun logo on the forehead and a green visor, with a small vertical slot beneath it that allows him to eat, drink, and smoke without removal, aided by a built-in toxin filter. His full battlesuit is made of a durable Spandex-like material, primarily red with a blue triangular chest patch bearing a yellow sun, white sections on the elbows and knees, white gauntlets and boots, and a white belt holstering his signature ray gun, the Sunshoot. Sunred seldom wears this uniform, opting instead for casual, weather-appropriate attire during fights. In his youth, as part of the Weather Three team, he dressed like a juvenile delinquent or beach bum in board shorts and camp shirts. He also possesses semi-formal wear, including a blazer-with-jeans combination and a business suit.

Jaded and disenchanted after his superhero career peaked and declined, Sunred is impatient, short-tempered, insensitive, thankless, selfish, vengeful, rude, and inconsiderate. He occasionally shows tenderness toward his girlfriend, Kayoko Uchida, and displays genuine enthusiasm for challenging battles against the Florsheim organization. He feels envy toward his colleagues’ successes and often directs his resentment toward Florsheim members through physical, verbal, and emotional abuse.

Sunred has no memory of his parents beyond their being deceased. He was formerly a member of Kishō Sentai Weather Three, a group resembling Sun Vulcan that disbanded due to internal conflicts, artistic differences, and romantic disputes. He remains in contact with Weather Blue, now a host-club host, and Weather Yellow, a construction worker. Sunred is part of a loose network of regional sentai heroes, including Kyōdai Senshi Abashirin, Shinrin Sentai Green Ranger, Shachihokoidā Great, and Tottori Senshi Sakyūn. As a senior hero, he mentors juniors like Sakyūn and Naitoman (later Naitōru). This hero network receives no government support, forcing Sunred to depend financially on Kayoko and occasional pachinko winnings. He sold his crimefighting motorcycle at a low price to cover expenses. Sentai heroes in his universe hold mid-level fame, below faded 1980s pop stars but above mid-level athletes in obscure sports.

Sunred shares a paradoxically stable relationship with General Vamp, leader of Florsheim’s Kawasaki branch. Despite Sunred’s constant abuse, Vamp works to improve the branch to better oppose him. Their interactions vary from Sunred inconveniencing Florsheim members to receiving homemade food or help with moving. Romantically, Sunred lives with Kayoko Uchida in her apartment and relies on her financially. Their relationship is strained by his terse and insensitive behavior, yet it endures partly due to Kayoko’s friendship with Vamp, who offers context for Sunred’s actions and advises her on being a better arch-nemesis.

Sunred possesses superhuman strength and durability, allowing him to brutally beat Florsheim monsters with minimal effort. His combat style incorporates kicks, punches, and Japanese pro-wrestling holds. He also has flame-based special moves, though these are only depicted in the series’ opening. His helmet provides immunity to inhaled toxins, poisons, and allergens—though not airborne germs—as well as telescopic vision (Red Eye) and enhanced hearing (Red Ear), which he often uses for eavesdropping. Despite his combat prowess, he lacks marketable non-superhero skills, though he is adept at improvised mechanical repairs without formal training.

As a child, Sunred was nicknamed “Sun-chan the Kappa” for his fondness for swimming.