Seiji Hokuto exists across multiple Ultraman franchise iterations, each with distinct backgrounds and roles. In the original *Ultraman Ace* series, Seiji was a truck driver delivering supplies to an orphanage. During an attack by the Terrible-Monster Verokron, he and nurse Yuko Minami perished while shielding children from harm. Their sacrifice prompted Ultraman Ace to resurrect them as dual hosts, granting Ultra Rings to fuse into the warrior. After Yuko departed to reunite with her lunar civilization, Seiji became Ace’s sole host, combating threats such as Yapool’s forces. He later joined cross-series missions, aiding Ultraman Taro against Alien Temperor and participating in events within *Ultraman Mebius* and *Ultraman Saga*, often guiding younger Ultras like Mebius through crises while embodying resilience and compassion. The *ULTRAMAN* manga and anime reimagine Seiji as a 16-year-old orphan surviving a plane crash engineered by terrorist Ace Killer, which claimed his parents. Severely injured, he was rescued by the alien Bemular and augmented with Yapool’s prosthetics. Donning the mechanized Ace Suit—equipped with thrusters, a Spacium Blade, and teleportation—he pursues vengeance as a vigilante. His clashes with Ace Killer and uneasy alliances with Shinjiro Hayata (son of the original Ultraman) highlight his impulsive tactics and moral ambiguity. Gradually transitioning from solitary avenger to reluctant teammate, he confronts adversaries like the Zetton Core and recurring foes, including a resurrected Ace Killer, while grappling with redemption. Key contrasts lie in their origins, alliances, and narrative focus. The original Seiji exemplifies selflessness and mentorship, whereas his reimagined counterpart navigates trauma and moral conflict through cybernetic enhancements. Both iterations uphold Ultraman Ace’s legacy but diverge in context, thematic exploration, and character evolution across their respective universes.