Rei Sakuma commands the idol unit UNDEAD as a third-year Yumenosaki Academy student under Rhythm Link. He bears a hereditary condition inducing sunlight sensitivity, daytime lethargy, and dietary reliance on iron supplements or blood substitutes, leading him to adopt a self-proclaimed vampire identity rooted in his family’s prideful embrace of vampiric mythology. Raised in isolation within a forested mansion by the secretive Sakuma clan, his condition barred outdoor activities, immersing him in books. This cultivated exceptional intellect, with adults seeking his counsel from childhood and inadvertently cementing a "god-like" reputation that distanced peers. His empathetic nature and compulsion to assist others strained relationships, particularly with childhood friend Keito. At Yumenosaki, Rei co-founded the anarchic unit DEADMANZ during his second year, later evolving into UNDEAD. He briefly served as student council president at Keito’s urging, a role designed to channel student resentment against him. His subsequent "study abroad" year involved seeking medical treatments for his brother Ritsu, resolving conflicts at Yumenosaki’s sister schools, and performing idol duties. This culminated in "The War," where adversaries Eichi and Ritsu exploited his compassion by orchestrating global crises to exhaust him, triggering his political downfall. Post-War, Rei adopted an "old man" persona, using archaic speech and feigned frailty to deflect expectations. He intensified his vampire affectation as emotional armor yet persistently meddled in others’ affairs. His self-neglect manifested in forgotten meals or consumption of expired tomato juice, necessitating oversight from UNDEAD members and associates. Rei’s journey centers on reconciling his humanity. Through UNDEAD’s activities—especially after the Repayment Festival—he gradually shed the "immortal vampire" facade, embracing human flaws. His leadership balances autonomy for strong-willed members Kaoru Hakaze, Koga Oogami, and Adonis Otogari with subtle guidance to foster their idol growth. His bond with Ritsu remains fraught. Rei’s overseas research travels made Ritsu feel abandoned, breeding hostility. Despite Ritsu’s harshness, Rei relentlessly pursues reconciliation, viewing atonement as lifelong penance. Their dynamic harbors mutual protection beneath surface tensions, evident during family rituals like Transylvanian New Year gatherings. Rei’s talents encompass jazz dance, multilingual fluency in English and sign language, and mastery of guitar, drums, piano, and violin. He enjoys night walks, gardening, and reading, with preferences for tomato juice, cured ham, and sweetened black coffee—playfully citing vulnerabilities to garlic, crosses, and holy water. In later career phases, he embraces new challenges while harmonizing his human identity with UNDEAD’s "immortal demons" philosophy, emphasizing profound human connections. His story culminates in renewed purpose, transcending past wounds through artistic expression and familial healing.