Yūki Hayabusa, a Koga clan ninja and sister to Kojiro, bears the scars of a tragic past: her family fell to the immortal cyborg Ginnai Doma during his assault on their village a year and a half before the central narrative. Though driven by a thirst for vengeance, her brother’s insistence on retreat left their shared grief unresolved, fueling simmering tensions between them. Aligning with rival ninja factions opposing Ginnai and Oda Nobunaga—a warlord wielding machine guns and cyborg soldiers far ahead of their time—Hayabusa repeatedly clashes with Shishimaru Tenoh, the protagonist. Their rivalry stems from his disdain for her clan and her reproach of his emotional fragility. Yet their combative dynamic evolves during joint missions to eliminate Ginnai, where her tactical ingenuity shines through coordinated ambushes and meticulously laid traps. A pivotal shift occurs when Nagatoji, a seasoned ninja, sacrifices himself to protect the group, tasking Shishimaru with safeguarding Hayabusa. This act forges reluctant trust, leading them to collaborate on a decisive rockslide ambush against Ginnai. Initially wary of partnership, Hayabusa gradually unites with Shishimaru’s quest for justice, confronting their mutual foe during the cyborg’s catastrophic reactor meltdown. In alternate timelines, Hayabusa serves as a 23rd-century temporal agent dispatched to rectify alien-induced distortions in the Sengoku period. Captured by Nobunaga’s cyborg allies Ulysses and Zhang Fei, she endures mental extraction for future intel before Ulysses, recognizing the conflict’s pointlessness, secures her release. Liberated, she allies with the Black Lion syndicate to counter cross-dimensional incursions, ultimately departing Earth alongside Shishimaru and the group to confront existential threats across the cosmos. Her journey arcs from singular vengeance to coalition-building, adapting as dangers escalate. Through fraught alliances and clashing ideologies, she navigates loyalty to her clan with the pragmatism of cross-faction unity, embodying resilience amid relentless adversity.