Natsumi Murakami occupies seat twenty-eight in Class 3-A at Mahora Academy. She belongs to the school's Drama Club, harboring a passion for acting often hindered by profound shyness and low self-confidence. Deep dissatisfaction with her physical appearance fuels this, particularly comparisons to roommates Ayaka Yukihiro and Chizuru Naba regarding her underdeveloped figure, along with struggles over her unmanageable hair and freckles (in the manga). Her initial portrayal stresses her ordinariness and absence of unique talents or magical abilities. Her trajectory shifts dramatically when she and Chizuru discover the injured Kotaro Inugami in his dog form. Pressured by Chizuru to convince Ayaka to let Kotaro stay, Natsumi pretends he is her younger brother, "Kotaro Murakami." Though initially reluctant, she gradually embraces the sibling role. Following the Mahora Festival, however, she exhibits jealousy towards girls Kotaro interacts with (Yue, Nodoka, Kaede, Mei, Takane), revealing burgeoning romantic feelings despite their frequent arguments born from mutual difficulty expressing emotions. Her significance amplifies during the Journey to the Magical World Arc. Concerned for Negi Springfield, she secretly travels to the Magic World. Separated from most companions at the Gateport and needing medicine for the ill Ako, Natsumi, Akira, and Ako incur a crushing 1,000,000 drachma debt. To repay it, they become slaves under a beastwoman called "Chief," bound by magical collars preventing escape but offering protection by recording harm. Witnessing Kotaro (disguised by age-changing pills) and Negi battle Jack Rakan in a tournament to win the prize money for their freedom reveals Kotaro's beast form to her. The prize secures their release, with Kotaro personally using the key to free Natsumi. Encouraged by Haruna to form a Pactio contract, Natsumi learns she could perform the contract kiss with Kotaro instead of Negi. This sparks intense introspection; comparing herself unfavorably to women like Mei Sakura, Kaede Nagase, and Chizuru Naba in Kotaro's life, she deems herself unsuitable. She attempts the Pactio by kissing Kotaro while he sleeps, only to be interrupted by Haruna, who failed to mention the ritual requires Chamo's presence. Later, at a Governor's Ball, Kotaro asks her to dance, heightening her confusion, partly due to his true age as a ten-year-old boy. Overhearing Kotaro complain about Haruna's Pactio suggestion, Natsumi flees in despair. Kotaro catches her, clarifying his reluctance stems from his youth and lack of readiness for romance, not her personally. When he questions if she likes him, she unconvincingly denies it. Kotaro then confesses he loves her, stating she is the most important person in his life at that moment. Bolstered, Natsumi successfully forms the Pactio contract. Immediately after, she shockingly confesses her own love aloud before running away, later worrying he didn't hear it and trying to keep it secret. Her artifact, "Actrix Timida" (Timid Actress), manifests as "Adjutor Solitarius" (Lonely Stagehand), creating illusions enabling her team to infiltrate areas like the Ostia Ruins undetected. During the final battle to rescue Asuna, Natsumi uses Adjutor Solitarius to help the team bypass enemies, including Fate Averruncus. She remains among the few not incapacitated during the retrieval of Asuna and the Great Grand Master Key, though she and Nodoka are later captured by Fate. Following the conflict, she assists Negi in the mission to save his father and defeat the Mage of the Beginning. In the epilogue, she pursues Kotaro to the Magic World after he departs for "ninja training," framing it as her graduation trip. During an adventure there, she demonstrates significant growth, effectively using her artifact to survive. Upon reuniting, she punches Kotaro seven times from a blind spot. They eventually marry in 2015, receiving their friends' blessings. Regarding "Mahō Sensei Negima! Anime Final," the film presents an alternate ending where Negi chooses one student as his permanent Pactio partner before the class's memories of magic are erased. Promotional material lists Natsumi among the cast.