Shiro Yusa, born March 3, 1990, manifests as the apoptosis of Ren Fuji—a self-destructive force born from Ren's subconscious yearning for death. Growing up adjacent to Ren and Kasumi Ayase, he initially maintained distance. At age six, driven by Ren's buried hatred, he stabbed and killed Kasumi's father, Mr. Ayase. Ren helped stage the death as an accident, exploiting the discovery of Mr. Ayase's basement torture chamber to ensure Kasumi and her mother remained oblivious to their guilt. Plagued by crushing boredom and agonizing precognitive déjà vu from Mercurius, Shiro relentlessly pursues extreme thrills to disrupt his sense of predestination. Reckless, foul-mouthed, and amoral, he wields sharp intellect and academic excellence yet acts without hesitation. He instigates fights freely, valuing excitement over ethics, though profound horrors evoke latent fear beneath his fearlessness. A year before the central events, a motorcycle accident obliterated his taste, smell, and pain senses while amplifying his others, fueling his thrill-seeking. Two months pre-story, his friendship with Ren shattered during a rooftop brawl after Shiro threatened to expose their crime to Kasumi, intending to destroy Ren's ordinary life. Hospitalized, he met Eri Honjou, the director's granddaughter, who aided his escape. Together, they seized control of The Bottomless Pit nightclub. Shiro's abilities escalate across timelines. His innate "Sense of Foreknowledge" grants precognitive déjà vu, enabling near-invulnerability when death feels improbable. Coupled with Mercurius-linked supernatural luck, he survives lethal scenarios and manipulates environmental factors. Acquiring holy relics unlocks further powers: in certain routes, Elizabeth Bathory (Die Blutgräfin) manifests chains with 10-ton force, transmutes his body into torture devices like an iron maiden ribcage, and enhances his Desert Eagle to inflict spiritual damage. His ultimate power, Atziluth "Malignant Tumor Apoptosis," activates upon pseudo-god ascension as an Observer. It suppresses all supernatural phenomena near him, reducing entities with lower Taikyoku than Ren to humans and forcing self-destruction upon weaker divine powers—allowing him to wound gods like Reinhard and Mercurius. The ability backfires against normal humans, nullifying his own powers. Route-specific outcomes diverge: in Kasumi's route, he sacrifices himself after defeating Wilhelm Ehrenburg to save her; in Kei's route, he survives Wilhelm but loses an arm to Wolfgang Schreiber; in Marie's route, Rusalka Schwägerin consumes him, yet he seizes her relic from within her body and later battles alongside Eri's spirit; in Rea's route, Wilhelm revives him post-mortem, leading to a rooftop confrontation with Ren where, embracing his role as apoptosis, Shiro shoots himself to enable Ren's final battle. His soul ascends as Observer of the Fourth Heaven, later joining the trinity god-battle by stealing souls from Reinhard's legion and firing divinity-weakening bullets. In Marie's route epilogue, Shiro reincarnates into a peaceful world, stripped of past memories. Within Kajiri Kamui Kagura's continuity, he and Eri reincarnate as Tenma Sukuna of the Yatsukahagi.