Ritsu Sakuma is a student at Yumenosaki Academy and an idol within the unit Knights, signed to the agency NEW DIMENSION. He belongs to the Sakuma family, carrying a hereditary condition manifesting as vampiric traits: severe sunlight sensitivity, chronic fatigue, low blood pressure, and blood cravings. Though human, he fully embraces a vampire persona, often playfully demanding blood as payment. He uses specialized umbrellas to navigate sunlight and is most active nocturnally, conducting midnight livestreams to engage fans. Born into a wealthy yet isolated household, Ritsu grew up in a forested mansion resembling a haunted house. With absent parents, his older brother Rei served as his primary caretaker. Highly intelligent but reclusive, Ritsu was initially homeschooled and solely dependent on Rei for companionship, resenting Rei's frequent absences which sparked recurring conflicts. He met Mao Isara during elementary school after Mao delivered a message to Rei. Ritsu reacted with hostility, attempting to drive Mao away using a rubber band gun. Rei later enrolled Ritsu in Mao's youth group, where Ritsu excelled academically and slowly formed a bond with Mao. Subsequent mansion renovations placed their homes adjacent, allowing Ritsu to visit Mao by climbing through windows. He stopped attending the youth group in middle school to focus exclusively on his friendship with Mao. Ritsu's personality blends lethargy with sharp perceptiveness. During the day, he often appears disinterested and fatigued, frequently napping in shaded spots. He initially distanced himself from classmates and idol activities, viewing them as burdens, and relied solely on Mao for emotional support. Yet, he reveals a playful, teasing side around trusted individuals and demonstrates acute observational skills, habitually psychoanalyzing others—a tendency he labels a "bad habit." He is blunt, occasionally harsh, and prone to jealousy, exhibiting possessiveness over close bonds like his friendship with Mao. Abandonment issues stemming from Rei's unexplained year-long overseas trip for medical research intensify his clinginess and emotional withdrawal. Despite this, he shows deep loyalty and protectiveness towards those he cherishes. Over time, Ritsu experiences significant development, evolving from an antisocial figure into an engaged member of Knights. He forges bonds with unitmates like Leo Tsukinaga, who describes him as "a bit of a handful" yet reliable, noting Ritsu's piano skills and clinginess, comparing him to a cat. As Knights' strategist, Ritsu contributes intellectually. By the !! era, he actively seeks ways to challenge his limitations, researching methods to participate in daytime idol work while maximizing nighttime activities like livestreams. His performances feature fluid, graceful movements and a soft, mellifluous singing voice. Ritsu's relationship with Rei remains complex, marked by resentment over Rei's departure, feelings of betrayal, and brusque, physically aggressive interactions. Despite this, Ritsu gradually comes to understand Rei's motivations and cares for him deeply. The brothers share vampiric traits, nocturnal preferences, and a habit of humorously acting superior to juniors. Ritsu maintains a lifelong friendship with Mao, teasing him as "dumb yet cute" but relying on him for practical support. Notable traits include his skill in baking (creating visually grotesque but delicious pastries), piano playing, and songwriting, which reveals a wistful, introspective side he seldom displays openly; he stress-bakes when overwhelmed. Academically, chronic lateness and napping led him to repeat his first year. His given name, meaning "cold moon," reflects his nocturnal nature, while his surname "Sakuma" references the new moon and temporal intervals.