Karen Araragi, Koyomi Araragi's eldest younger sister born roughly four years before him, shares an exceptionally close bond with her younger sister Tsukihi. Together, they formed the self-proclaimed "Fire Sisters" at Tsuganoki 2nd Middle School, gaining popularity by intervening in incidents to help others. In childhood, Karen was more delicate and sensitive; thoughtless remarks from Koyomi once nearly drove her to suicide. This trauma profoundly shaped her extreme, unwavering sense of justice, fueling her commitment to being a "hero of justice." She recalls playing with Nadeko Sengoku, invited by the sisters, and remembers Sodachi Oikura briefly living with the Araragi family—a memory Koyomi lacks. Physically, Karen stands tall at 170 cm, surpassing Koyomi in height. She has black hair, typically tied in a wavy right-sided ponytail, gray eyes, and an ahoge like her siblings. Her iconic outfit features a yellow and black hooded tracksuit over a black tank top, matched with shorts, red knee-high socks, and sneakers. She cut her ponytail short during the Tsukihi Phoenix arc, later regrowing it. A temporary physical change during Koyomi Reverse rendered her body more petite. Karen displays a dual personality: publicly, she is lively, tomboyish, confident, and popular, often adopting tokusatsu-inspired hero mannerisms to maintain a cool image. Privately, especially around Koyomi, she reveals a goofy, airheaded side, speaking without filtering her thoughts. Her sense of justice, lacking Koyomi's cynicism, appears more innocent yet occasionally naïve to him. She tends to suppress insecurities and avoid relying on others, mirroring Koyomi's flaws. Athletically gifted, Karen holds a karate black belt and practices capoeira among other martial arts. Her physical prowess enables her to defeat Koyomi despite his residual vampiric strength, though she acknowledges being outmatched by specialists like Yozuru Kagenui. Key story involvements include confronting con man Deishuu Kaiki during the "Karen Bee" arc, believing he scammed students with fake charms. Kaiki easily overpowered her, inflicting a cursed fever via a flame-wreathed bee. This led to a physical fight with Koyomi, who intervened against her wishes. It was later revealed Karen and Tsukihi acquired boyfriends partly to provoke Koyomi's jealousy, with Karen dating a shorter boy named Mizudori. In "Yotsugi Doll," Karen and Tsukihi were kidnapped alongside Suruga Kanbaru by Tadatsuru Teori, requiring rescue by Koyomi and Yotsugi Ononoki. By "Suruga Devil," Karen entered high school, dissolving the active "Fire Sisters" partnership. Her relationship with Koyomi deepened, causing concern for Kanbaru about its intensity. As an adult, Karen became a police officer, utilizing her martial arts skills. She forged many friendships, serving as a "mood maker" in her department while retaining her bright, cheerful demeanor. Her bond with Tsukihi remained central, while her friendship with Kanbaru evolved from initial idolization of Kanbaru's athletic prowess into mutual reliance. Her dynamic with Koyomi shifted from conflict to mutual support, particularly during crises. A notable quote encapsulates her philosophy: "You can lose the match and the game, but if you don’t lose to yourself, it isn’t a loss."