Saitama is a bald, average-height man with a lean athletic build, originally depicted with short black hair before rigorous training led to complete hair loss. His signature yellow jumpsuit hero costume features a black belt, red gloves, red boots, and a white cape secured by round buttons. His appearance shifts stylistically between comedic and serious tones, morphing from a cartoonish simplicity to sharply detailed musculature and intense expressions during combat.
Three years before becoming a hero, Saitama was an unemployed office worker who impulsively saved a child from the monster Crablante. This act spurred him to pursue superheroism through a grueling daily regimen: 100 push-ups, 100 sit-ups, 100 squats, a 10 km run, and abstaining from climate control, which granted unparalleled power at the cost of his hair. Early struggles included battles against foes like the Personification of a Light Pull Cord and Octopus Claw Man, during which he sustained injuries that charted his evolution from ordinary to invincible.
Officially registered as "Caped Baldy" in the Hero Association’s A-Class Rank 39, Saitama’s record-breaking physical exam scores were offset by low written test results, relegating him to lower tiers. He routinely lets others claim credit for his victories, such as attributing the Deep Sea King’s defeat to weakened heroes or anonymously aiding police during monster attacks.
His power borders on invulnerability, enabling feats like obliterating a meteor with one punch, leaping from the moon to Earth, and countering Boros’ planet-level attack with a "Serious Punch." He survives vacuum exposure and withstands assaults from Cosmic Fear Mode Garou, who mimicked his abilities. Despite this, he avoids lethal force against humans, opting to subdue them non-fatally.
Apathy defines Saitama’s demeanor, his existential crisis stemming from a lack of worthy foes dampening emotional engagement. He fills downtime with gaming, bargain hunting, or TV, indifferent to fame. Yet he exhibits sharp tactical insight, dismantling manipulative tactics like Fubuki’s or recognizing Garou’s latent heroism. Baldness-related insults provoke rare irritation, and bargain sales often override hero duties, as seen against Carnage Kabuto.
His moral code prioritizes selfless action, defending cities like Z-City regardless of public opinion or personal risk. Though reluctantly mentoring Genos, he guides others with pragmatic advice. Relationships with figures like Speed-o’-Sound Sonic and King reveal a blend of detachment and latent responsibility, critiquing superficial hero rankings while upholding the core duty to protect.
Key growth moments include empathizing with Boros’ futile search for a rival and confronting Garou, whom he identified as a conflicted idealist craving validation. During these clashes, Saitama’s power surged exponentially, outpacing Garou’s copied techniques through escalating emotional drive. His journey remains a balancing act between mundane routines and the weight of unmatched power, continually seeking purpose beyond effortless victory.