Natsumi Murakami is a shy and insecure student in Class 3-A at Mahora Academy, harboring a passion for acting within the school's drama club. She grapples with significant self-esteem issues stemming from her physical appearance, including an underdeveloped figure, unmanageable hair, and freckles (in the manga), feelings intensified by living alongside roommates Ayaka Yukihiro and Chizuru Naba, both possessing more mature physiques. Her trajectory shifts during the Training/Graf Wilhelm Arc when she and Chizuru discover the injured Kotarou Inugami in his canine form. Pressured by Chizuru, Natsumi agrees to pretend Kotarou is her younger brother, "Kotaro Murakami," allowing him to stay in their dormitory. Though initially a ruse, Natsumi adapts to the role and later exhibits romantic jealousy towards Kotarou's interactions with Yue Ayase, Nodoka Miyazaki, Kaede Nagase, Mei Sakura, and Takane. Natsumi's journey expands significantly in the Journey to the Magical World Arc, following Negi Springfield into Mundus Magicus. Separated during an attack, she, Akira Okouchi, and Ako Izumi reach Granicus City. When Ako falls critically ill, Natsumi enters debt slavery to secure vital medicine, accruing a 1,000,000 drachma debt. She and her friends are enslaved under relatively safe conditions by the benevolent beastwoman "Chief," wearing explosive collars to prevent escape. Kotarou and Negi later secure her freedom using tournament prize money. Encouraged by Haruna Saotome, Natsumi attempts to form a Pactio contract (sealed by a kiss) with Kotarou but initially fails due to misunderstandings. After mutual confessions of love during a confrontation, they successfully establish the Pactio. This grants her the artifact card "Actrix Timida" (Timid Actress), manifesting as "Adjutor Solitarius" (Lonely Stagehand), providing stealth capabilities crucial for infiltrating enemy territory during the final battle to rescue Asuna Kagurazaka and retrieve the Great Grand Master Key. Her development culminates in marriage to Kotarou in 2015, as shown in the manga's epilogue. Their relationship, initially marked by mutual difficulty expressing feelings, evolves through shared adversities, including Natsumi's solo adventure in the Magic World after graduation to find Kotarou following his departure for "ninja training." Minor trivia includes her habit of secretly smelling Kotarou's shirts, which she denies when confronted by Chizuru.