Guren Ichinose, a pivotal figure within the Ichinose family—a subordinate branch of the Hīragi-led Imperial Demon Order—was born in Tokyo on August 28, 1996. Systemic discrimination marked his upbringing due to his lineage, intensifying after forging a forbidden bond with Mahiru Hīragi, a scion of the ruling clan. Their childhood friendship, laced with romantic tension, provoked violent retaliation from the Hīragi family, leaving lasting physical and psychological scars that fueled his rebellion against the oppressive hierarchy. At First Shibuya High School, Guren masked his true potential while covertly plotting against the Hīragi regime. During this period, he forged critical alliances with Shinya Hīragi, Mito Jūjō, and Norito Goshi, laying the groundwork for his future faction. A turning point arose when Mahiru, corrupted by her demon weapon, triggered a cataclysmic chain of events culminating in the apocalyptic "Catastrophe." Driven by guilt, Guren resurrected his deceased comrades at the cost of annihilating 90% of humanity, cementing his dual legacy as both architect of ruin and reluctant savior. As Lieutenant Colonel of the Japanese Imperial Demon Army, Guren commands the Moon Demon Company and leads the Guren Squad with cold pragmatism, masking internal turmoil beneath strategic efficiency. He recruits and trains Yuichirō Hyakuya, Shihō Kimizuki, Yoichi Saotome, and Mitsuba Sangū, arming them with Black Demon Series weapons while secretly wielding Mahiru-no-Yo—a sentient demon katana forged from Mahiru’s soul. This pact grants heightened power but risks possession by a merciless alter ego willing to sacrifice allies for strategic victories. Physically, Guren’s 183 cm frame mirrors his military rank and fractured psyche: black hair frames violet eyes that shift crimson under Mahiru-no-Yo’s influence. His attire evolves from a student’s gakuran to a double-breasted black officer’s coat adorned with gold insignia and ceremonial elements. The Mahiru-no-Yo katana, etched with a crimson streak, serves as both weapon and haunting reminder of his tether to Mahiru and the moral compromises defining his path. His motivations hinge on key relationships. An enduring fixation on Mahiru drives demonic pacts and clandestine experiments like the Seraph of the End project. Precarious alliances with Shinya Hīragi and Kureto Hīragi balance mutual distrust with shared objectives, while strategic pacts with vampires Ferid Bathory and Krul Tepes underscore his readiness to breach ethical limits. Though manipulative, he shields subordinates from brutal truths, veiling harsh realities to preserve their resolve. Across narratives, his arc centers on sacrificial atonement. The light novel *Resurrection at Nineteen* chronicles his quest to undo the Catastrophe’s fallout, clashing with entities like the Hyakuya Sect and the ancient Seraph Shikama Dōji. Manga and anime iterations trace his leadership in vampire conflicts, juggling military obligations with covert schemes. Ultimately, his journey culminates in a morally ambiguous leader entangled in cycles of betrayal and violence, striving to redeem past sins while safeguarding humanity’s fragile survival.