Shirou Yusa, born March 3, 1990, manifested as the Apoptosis of Ren Fujii, birthed from Ren's subconscious desire for death. He grew up as neighbors with Ren and Kasumi Ayase in Suwahara City, though their childhood interactions remained sparse. At age six, acting upon Ren's buried hatred, Shirou murdered Kasumi's father, Mr. Ayase. Ren helped cover up the killing, staging it as an accident, a secret kept from Kasumi and her mother. Two years prior to the main events, Shirou, Ren, and Kasumi relocated to Suwahara City, occupying adjacent apartments. Shirou created a passage through the wall between his apartment and Ren's for constant access. A year before the primary story, Shirou survived a catastrophic motorcycle collision that permanently destroyed his senses of taste, smell, and pain, while slightly heightening his remaining senses. This trauma awakened a supernatural "Sense of Foreknowledge," granting him persistent déjà vu and genuine precognition. This constant awareness fueled intense boredom with ordinary life, driving him to seek extreme thrills. Two months before the main events, Shirou threatened to expose the truth about Kasumi's father's murder to shatter their mundane existence, provoking a brutal rooftop fight with Ren that hospitalized them both. Recovering in the hospital, Shirou met Erii Honjou, the director's granddaughter, who aided his escape. Together, they seized control of an underground nightclub named "The Bottomless Pit." As Ren's Apoptosis, Shirou possessed inherent advantages: indefinite resurrection until fulfilling his purpose of killing Ren, and foreknowledge granting inhuman reflexes and tactical precision. He exhibited abnormally high luck in lethal situations, often perceived as divine intervention. In combat, he wielded conventional weapons—a Desert Eagle pistol, Honda Valkyrie Rune motorcycle, claymore mines, dynamite, and liquid nitrogen—deploying them strategically against supernatural enemies. His capabilities expanded dramatically upon acquiring Ahnenerbe relics: * In the Kei and Marie routes, he obtained Elizabeth Bathory (originally Rusalka Schwägelin's relic), manifesting as chains extending 20 meters with 10-ton tensile strength, needles fired as projectiles, a spiked torture wheel, and an iron maiden formed from his own ribcage to ensnare foes. His pistol gained limitless ammunition and soul-rending properties. * In Rea's route, after Wilhelm Ehrenburg's demise, he claimed Qliphoth Bacikal, gaining blood manipulation to create life-draining stakes and enhancing his pistol with similar effects. Route-specific events determined his fate: * Kasumi Route: Shirou died from fatal injuries sustained while defeating Wilhelm Ehrenburg to protect Kasumi. * Kei Route: He survived encounters with Wolfgang Schreiber by deducing Schreiber's weakness, luring him into a minefield, and sacrificing his own arm to deliver a critical blow. * Marie Route: Consumed by Rusalka, he seized her relic from within her body and later fought alongside Erii's spirit against Schreiber. * Rea Route: After temporary death and revival by Wilhelm, Shirou fully embraced his Apoptosis role. He forced Ren into a final confrontation on their school rooftop. Losing the fight, he shot himself to sever his connection to Ren and empower Ren's battle against Reinhard. During the divine conflict, his Atziluth—"Malignant Tumor Apoptosis"—suppressed all supernatural powers weaker than Ren's, neutralizing divine legions and briefly equalizing the clash between gods. His soul was ultimately absorbed into Gladsheimr. In the epilogue of Marie's route, Shirou reincarnated into a peaceful existence with Erii and others, devoid of past memories. His ultimate legacy continued through Tenma Sukuna, his and Erii's reincarnation in Kajiri Kamui Kagura. Personality-wise, Shirou was a thrill-seeking genius perpetually bored by normalcy. His actions lacked conventional morality, driven primarily by alleviating his existential ennui. Despite his reckless, confrontational nature and sharp tongue, he harbored underlying fear when confronting true horrors. His relationship with Erii Honjou evolved into a romantic partnership, while his bond with Ren remained complex—marked by rivalry, mutual destruction, and reluctant loyalty.