Shirō Emiya's origins lie in the childhood trauma of the Fuyuki City fire, which killed his parents and left him mortally wounded. Kiritsugu Emiya saved him by embedding the sheath Avalon into his body and later adopted him. Kiritsugu's philosophy of becoming a "Hero of Justice" deeply shaped Shirō, who vowed to fulfill this ideal despite receiving only basic and incomplete magecraft training. This upbringing fostered a distorted self-worth centered on self-sacrifice, survivor's guilt, and a compulsive need to help others regardless of his own safety. His daily life involved excelling at housework, cooking, and part-time jobs, while maintaining relationships with figures like Taiga Fujimura and Sakura Matou, who frequently visited his household. During the Heaven's Feel route, specifically in *lost butterfly*, Shirō faces a critical divergence. After losing his Servant Saber to the Shadow and sustaining injuries, he prioritizes protecting Sakura Matou above all else, abandoning his lifelong ideal of heroism. This follows learning about Sakura's suffering: her body hosts Crest Worms implanted by Zōken Matou, and she is the unintended source of the Shadow—a manifestation of the corrupted Holy Grail consuming Masters and Servants. Shirō's resolve to shield Sakura intensifies despite warnings from allies like Rin Tohsaka and Kirei Kotomine about the Grail's corruption and the danger she poses. A pivotal development occurs when Rin's Servant, Archer, sacrifices himself battling the Shadow. Archer severs his own left arm and grafts it onto Shirō to save his life. This arm contains Archer's powers and memories, but its overwhelming magical energy causes severe physical degradation. A holy cloth seals the arm to mitigate this, though sporadic use accelerates Shirō's bodily breakdown. The transplant forces him to confront Archer's cynical worldview, yet Shirō rejects this perspective, reinforcing his commitment to Sakura. Shirō's relationship with Sakura forms the emotional core of his arc. He openly affirms his romantic feelings for her, leading to increased intimacy. However, Sakura's instability grows due to the Crest Worms' influence and her guilt over the Shadow's killings. When Sakura retreats to the Matou residence, Shirō pursues her and intervenes during Shinji Matou's attempted assault. This triggers Sakura's breakdown; she kills Shinji and merges with the Shadow, transforming into Dark Sakura. Throughout this turmoil, Shirō's actions remain driven by a singular focus: protecting Sakura at any cost, even as his physical and ideological foundations crumble. Shirō's character evolution contrasts sharply with other routes. While the Fate route reinforces his self-sacrificial ideals and Unlimited Blade Works moderates them through pragmatism, Heaven's Feel sees him wholly forsake heroism for personal love. This path culminates in irreversible choices, such as ignoring Zōken's ultimatum to kill Sakura and enduring the consequences of Archer's arm. His development underscores a shift from abstract justice to tangible, albeit fraught, human connection.