Katsumi Nakase, widely recognized by her cosplay alias Fubuki, is a second-year high school student and close friend to Mayuri Shiina, Kaede Kurushima, and Yuki Amane. She first met Mayuri at a cosplay event where Mayuri sewed costumes for her, sparking their friendship. Nakase often cosplays male characters due to her naturally boyish appearance, which notably drew significant female attention during a 2009 event where she portrayed Seira Orgel from *Blood Tune*. While maintaining friendships at school, she remains the only one in her group without a boyfriend. Physically, Nakase has short, light brown hair cut in a fringed bob and light brown eyes. She stands 158 cm tall with a slim 48 kg frame and measurements of 82-52-79 cm. Her typical outfit includes a bright-yellow jacket featuring black zigzag patterns on the sleeves, layered over a beige hoodie and a pink shirt. She chafes at her boyish looks, which influence her cosplay choices. Energetic and tomboyish, Nakase nonetheless enjoys cute outfits and activities. She is notoriously flirtatious with Mayuri, making provocative remarks like wanting to "lick her forever," and exhibits similar behavior towards her other friends. Her demeanor is brash and unfiltered; she speaks impulsively, struggles with lying, and cannot keep secrets. An otaku, she shares anime and video game interests with Mayuri. Socially adept, she befriends fellow patients quickly during hospital stays. Nakase harbors a strong dislike for Itaru Hashida, frequently calling him a pervert and rejecting comparisons. Among her relationships, Nakase feels closest to Kaede, viewing her as an older sister figure after two years of friendship. She admires Yuki's beauty and occasionally joins her for cooking lessons with Mayuri and Kaede. Her interactions with Rintaro Okabe are less intimate; she sometimes hints at wanting a relationship between him and Mayuri but keeps a respectful distance. Okabe visits her in the hospital primarily with Mayuri to avoid misunderstandings. She knows Faris Nyannyan and Luka Urushibara through Mayuri but lacks significant ties. Nakase's involvement spans world lines. In the *Steins;Gate* visual novel, she meets Mayuri at a Starbucks on August 13 in Alpha world lines for costume adjustments. In *Steins;Gate 0*, she becomes playable during the *Closed Epigraph* chapter, socializing with friends. She contracts an encephalitis variant, developing heightened Reading Steiner. This triggers flashbacks to Mayuri's repeated Alpha Attractor Field deaths and visions of World War III in Beta world lines. During a Christmas party, she and Okabe collapse during a shift to a world line where World War III erupts prematurely. Interrogated by a man named Shimoyama, she inadvertently reveals knowledge of an alternate world line where the USSR survived. Hospitalized afterward, Okabe confides in her about Reading Steiner and world lines—information later extracted by Professor Alexis Leskinen, implied to involve brainwashing. In a World War III world line, she sustains injuries during the Great Bombing of Tokyo before reuniting with Okabe. In the spin-off *Steins;Gate: Linear Bounded Phenogram*, her older brother Shinichi Nakase appears as a cosplayer infatuated with Mayuri. Though Nakase doesn't feature directly, Shinichi's involvement ties to her family. During a *Steins;Gate 0* gift exchange, she gives Okabe "baby doll lingerie," suggesting Mayuri wear it or, when refused, teasingly proposing he wear it himself. Rumors about her dating Okabe surface during a hospital visit, which both deny. Her name combines "overcome" (克, *katsu*) and "fruit/truth" (実, *mi*), with her surname meaning "middle" (中, *naka*) and "rapids" (瀬, *se*).