Seina Yamada hails from Earth, where his family runs a small grocery store in Okayama, Japan. He shares a lifelong bond with Tenchi Masaki, Kiriko Masaki, and her brother Kai, yet endures social isolation due to an extreme supernatural propensity for misfortune. This "biased probability" manifests as constant minor disasters, causing others to actively avoid him. His life changes dramatically when a Galaxy Police (GP) spaceship piloted by Amane Kaunaq crashes near him. Amane intended to recruit Tenchi but mistakes Seina for Tenchi's apprentice, giving him the GP application instead. Seina's family, misinterpreting the form as a contest entry, forcibly obtain his signature and thumbprint. He awakens aboard a GP vessel, officially enrolled against his initial wishes. Initially facing resistance within the GP due to Earth's underdeveloped status, Seina gains crucial backing from influential figures: Seto Kamiki Jurai ("Devil Princess of Jurai") recognizes his bad luck's strategic value for attracting space pirates, and GP Board Director Airi Masaki also supports him. Despite Kiriko's protective objections, he remains in the academy. His training includes mandatory body-enhancement surgery, granting superhuman strength but requiring significant adjustment to control his movements. The GP capitalizes on his misfortune by assigning him to command the decoy ship *Kamidake*. His presence reliably lures pirate fleets, leading to record captures. After the *Kamidake* is destroyed by pirate Tarant Shank, Seto provides Seina with the advanced *Kamidake II*, designed by Washu Hakubi. This ship integrates a cabbit named Fuku as its power source and biological computer. Later, under Seto's supervision, the ship fuses with Kiriko Masaki's second-generation Juraian Royal Tree, "Mizuki," gaining the ability to generate protective Light Hawk Wings. As captain, Seina earns a fleet commander's salary. While his cadet status restricts access to the principal, the accrued interest transforms his family's business into a large supermarket and funds a new home. His crew includes Amane (weapons specialist), Kiriko (systems operator), Ryoko Balta (pilot—a reformed pirate who quit the Daluma Guild after falling for Seina), and Neju Na Melmas (a 2000/3000-year-old former high priestess resembling a child who develops romantic feelings for him). These women, alongside others like Fuku and later Seto's handmaidens, form complex romantic entanglements around him, though he remains largely oblivious and initially resistant to their advances. A critical mission to rescue Fuku from Tarant Shank and rogue Galaxy Army factions strands Seina on a planet inhabited by the Wau tribe. They identify him as a prophesied hero and thrust him into "Idol," an ancient mecha. Activating the mecha, he saves Fuku and her cloned siblings, integrating it with the captured *Kamidake II*. Notably, the mecha generates Light Hawk Wings independently of Mizuki. Emperor Azusa Jurai and Empresses Funaho and Misaki later reveal the mecha's power source is a first-generation Jurai Royal Tree seed, which bonds with Seina. This makes him third in line for the Jurai throne, behind Yosho and Tenchi Masaki. This lineage necessitates a political marriage to Amane, Kiriko, Ryoko, and Neju. Seina initially opposes it, perceiving coercion, but accepts after confirming the women's genuine affection and consent. During the wedding preparations, Tarant Shank attempts assassination but is subdued by Seina. Simultaneously, Seto's four ladies-in-waiting—Gyokuren, Hakuren, Karen, and Suiren—reveal themselves as agents of the non-aligned Renza Federation. To secure their homeland's alliance with Jurai, they kidnap Seina and publicly initiate intimate contact, forcing their inclusion in the marriage for political stability. Consequently, Seina marries all eight women (Amane, Kiriko, Ryoko, Neju, and the four Renza agents), with Fuku also often included as part of his bonded family unit. He continues commanding the *Kamidake II* with his wives as crew, patrolling against pirates. The GXP light novels provide additional depth, as explored by creator Masaki Kajishima. Seina subconsciously develops heightened reflexes and danger-sensing abilities as a survival mechanism against his luck. He is revealed as the reincarnation of Kazuki. Furthermore, Washu discloses that Tenchi Masaki's latent power inadvertently granted Seina and his harem immortality, alleviating Tenchi's fear of eternal solitude. The novels also explore Seina's profound guilt, believing his bad luck contributed to the death of Tenchi's mother, Kiyone Masaki. His character evolves from a perpetually unlucky Earth boy into a respected GP captain, Juraian royalty, and patriarch of a large polygamous family, leveraging his once-debilitating curse for galactic law enforcement while navigating complex political and personal relationships.