Seabook Arno begins life as an engineering student on Frontier IV. His world shatters during the Crossbone Vanguard's assault, forcing him to flee his colony with his sister and friends. They find refuge aboard the Earth Federation training ship Space Ark at Frontier I, where urgent circumstances thrust Seabook into the cockpit of the prototype F91 Gundam to defend the vessel. Demonstrating remarkable combat aptitude from his first sortie, he swiftly destroys multiple enemy mobile suits. This prowess fuels crew speculation about potential Newtype abilities, heightened by the F91's bio-computer system designed by his estranged mother, Monica Arno – his bitterness stemming from her prioritizing research over family. Reluctantly accepting his role as a pilot, Seabook's skills grow through combat and emerging Newtype sensitivities. He masters the F91's advanced systems, including beam shields, the Variable Speed Beam Rifle (VSBR), and its distinctive heat management enabling rapid maneuvers via armor ablation. While protecting allies and opposing the Crossbone Vanguard's aristocratic Cosmo Babylonia movement, he grapples with personal conflicts, particularly his resentment toward his mother. A pivotal confrontation sees him defeat faction leader Carozzo "Iron Mask" Ronah by turning the Rafflesia mobile armor's own firepower against it. A decade later, operating under the alias Kincade Nau, he collaborates with Cecily Fairchild to rebuild the Crossbone Vanguard as a resistance force against the Jupiter Empire. Mentoring young pilot Tobia Arronax and piloting the XM-X1 Crossbone Gundam X-1, he forms a tense alliance with former adversary Zabine Chareux. Combat against the Empire sees Zabine damage the X-1's cockpit, sending Seabook crashing to Earth. Rescued by the Strategic Naval Research Institute (SNRI), he sustains injuries requiring a mechanical prosthetic for his right arm and bears a scar over his right eye. Despite these wounds, he returns to the conflict. His final duel against Zabine results in the destruction of the X-2 and Zabine's death. Following the conflict, Seabook retires to Earth, marries Cecily, and establishes a bakery. They have at least one child. Photographs suggest a peaceful existence, though he remains tangentially involved; when Tobia considers recruiting him for the Steel 7 mission to Jupiter, he learns Seabook is celebrating the birth of a second child and chooses not to disturb his family. Two decades later, during the Zanscare Empire's invasion, Seabook shelters with his community in a sports dome. He encounters Font Bow and Belle, discerning Belle's lineage as daughter of Curtis Ruthko and Tetenith Dogatie. Taking Belle on as a bakery apprentice, he helps her bake bread to support Font. Later, he borrows the XM-X0 Crossbone Gundam X-0 to repel Zanscare remnants threatening his town. He provides Font with bread for Curtis, concluding his recorded actions.