Koyomi Araragi is a third-year high school student who, after surviving a vampire attack over spring break, regained most of his humanity but kept several vampiric traits, including enhanced regeneration, superhuman strength, and improved vision. He maintains a connection to Shinobu Oshino, the vampire who turned him, and continues to provide her with his blood. His parents are both police officers, and he has two younger sisters, Karen and Tsukihi Araragi. The family upholds a powerful sense of justice, cultivated through strict parenting that often made him feel ashamed when he fell short of those ideals. As a child, he briefly lived with Sodachi Oikura, a girl escaping an abusive home, though he later forgot this period. They met again in middle school, when Sodachi tutored him in math and tried to hint at her ongoing domestic struggles through unusual study conditions. He pretended not to understand, unwilling to involve his parents due to his strained relationship with them at the time. In his first year of high school, a cheating scandal arose in his math class. Sodachi, then the class representative, had held a study session before an exam; attendees scored unusually well. Suspecting foul play, she called for a class trial. As the chairman, Araragi failed to manage the discussion, and a majority vote wrongfully placed blame on Sodachi, though the teacher was actually responsible. The event left him deeply scarred, solidifying his belief that friendships would compromise his integrity. He adopted a solitary lifestyle for much of high school, his grades slipping aside from math, which he excelled in thanks to Sodachi’s earlier lessons. Near the end of his second year, Tsubasa Hanekawa broke through his isolation and became his first friend. Soon after, he encountered the severely weakened vampire Kiss-Shot Acerola-Orion Heart-Under-Blade. Initially refusing her request for blood, he eventually yielded to her pleas and offered himself to save her. Instead of letting him die, she turned him into her thrall. With Meme Oshino’s guidance, he fought three vampire hunters to reclaim Kiss-Shot’s limbs. After restoring her, he was appalled by her true nature and tried to kill her. A compromise mediated by Meme Oshino allowed him to absorb most of her power, reverting her to a childlike form known as Shinobu Oshino and returning him to a near-human state, permanently bound to her. As a third-year, he served as class vice president and started assisting girls affected by supernatural oddities, which often reflected their psychological struggles. He entered a romantic relationship with Hitagi Senjougahara. His willingness to help others at great personal risk became a defining quality, though some interpreted it as a selfish desire to be perceived as a savior. This behavior stemmed from his ingrained sense of justice and lingering self-reproach over past failures. His unresolved history with Sodachi Oikura reemerged in his third year, compelling him to admit that he had recognized her distress but deliberately ignored it. This realization unfolded through interactions with Ougi Oshino, who was ultimately revealed as a manifestation of his own self-critical thoughts and insecurities. Acknowledging Ougi as part of himself marked a pivotal moment in accepting his identity and imperfections. After high school, he attended college and continued his relationship with Hitagi Senjougahara, though it included periods of separation and reconciliation. His post-graduation narrative centered on the ongoing struggles of the girls he had helped, and he engaged in solving further oddity-related cases, including those involving vampiric mummies. Physically, he has black hair that often covers one eye, grey eyes, and a medium complexion. Over time, he grew his hair longer to conceal vampire bites on his neck. His physique is muscular, a remnant of his vampirism, and he typically wears his school uniform or casual clothing like hoodies and jeans. Like his sisters, he has a highly expressive ahoge that shifts shape with his emotions. His abilities are largely tied to his residual vampirism, including a potent healing factor that intensifies when he gives blood to Shinobu. At the height of his vampiric power during spring break, he was extraordinarily strong but still vulnerable to traditional vampire weaknesses. He also acquired the ability to create new aberrations, a power indirectly inherited from Tooe Gaen via a complex sequence involving the Rainy Devil and Shinobu. He used this ability to form both Ougi Oshino and the Mirror World. He is referred to by various names, including Araragi-kun, Araragi-senpai, Koyomi, and occasionally derogatory terms like "devilish boy," reflecting the varied dynamics of his relationships.