Muramasa is depicted as a young girl with short black hair, styled in a neat bob cut that reaches her jawline; in the manga adaptation, her hair appears with a purple hue. She has distinctive lavender-colored eyes and a slender build, accentuated by her noticeably large bust.

Her attire is traditionally Japanese, as she is almost always seen wearing a kimono or yukata, paired with classical wooden sandals and an obi. A small satchel is tied to the back of her waist, which she uses to carry her writing essentials such as notebooks and pencils.

A notable detail is the recurring bandages on the fingers of her right hand, a result of her obsessive dedication to writing often pushing herself to the point of injury. During her visit to Taiwan, Muramasa is shown in a more casual look, donning a sun-dress and carrying a parasol to shield herself from the sun.

Muramasa Senju is portrayed as an intensely self-driven and uncompromising novelist who prioritizes personal fulfillment over reader satisfaction. She writes exclusively for herself, often disregarding the conventions of publishing such as titling her works, a task she routinely leaves to her editorial team. Her writing process is spontaneous and all-consuming; whenever inspiration strikes, she begins writing immediately and becomes oblivious to her surroundings, regardless of time or place.

Highly critical of other authors, Muramasa openly expresses disinterest in her contemporaries, whom she considers dull and forgettable. This is exemplified in her dismissive attitude toward Elf Yamada, whose name she repeatedly forgets despite multiple encounters. Muramasa even critiques Elf’s work, describing her novel Bakuen no Dark Elf as boring. She has no memory of being invited on promotional trips such as to Taiwan further emphasizing her single-minded focus on her craft. The only writer she holds in high regard is Masamune Izumi, whose work she both admires and aspires to match.

Muramasa’s ultimate dream is to create as many novels as possible that she herself finds “the most interesting in the world.” Her admiration for Masamune borders on obsession, particularly after learning he planned to abandon the battle genre in favor of romantic comedies a shift that deeply disappointed her. During their first meeting, she appeared cold and dismissive of his goals, hoping to reignite his passion for writing battle-centric light novels. However, after learning more about his background, Muramasa revealed her genuine affection not only for his writing but for Masamune himself.

Although she was ultimately rejected, Muramasa continues to pursue him and sees Elf Yamada as a romantic rival. Despite her aloof and disinterested demeanor, she is quite shy and traditionally feminine at heart. She dislikes revealing clothing, such as bikinis, and is surprisingly bashful in romantic contexts. Her rare smiles are usually reserved for moments shared with Masamune, while her interactions with Elf are often filled with suspicion, irritation, and jealousy.

Little is revealed about Muramasa Senju’s early life, but it is known that she was raised in a frugal and financially conservative household. Her family often scolded her for spending excessive time writing, yet instilled in her a strong sense of financial restraint advice she continues to follow. Despite their disapproval, Muramasa remained devoted to her passion for storytelling.

Though highly knowledgeable in literature and creative writing, Muramasa is notably inept when it comes to technology and modern conveniences. She avoids using cash cards, struggles with touch-screen systems, and remains largely unaware of her surroundings. Curiously, she is proficient in using a computer, which she primarily utilizes for storing and reading novels.

For Muramasa, reading is more than a pastime it is the ultimate form of entertainment. She firmly believes that a truly perfect book, tailored specifically for a reader, can surpass anime, games, films, and even romantic love. Unable to find such a book in stores, she took it upon herself to write it. Before her debut as a professional author, she was an avid reader of Masamune Izumi’s early work during his time as a web novelist. Her admiration for him led her to memorize intricate details from all his stories and save them meticulously on her computer.

Unlike authors such as Elf Yamada or Masamune Izumi, who write for their audiences, Muramasa writes solely for herself. She agreed to become a professional light novel author only after realizing it would allow her to write freely without familial interference. One of her early career highlights was receiving a fan letter that praised her book as “a million points out of a hundred,” deeply inspiring her. Since then, her dream has been to craft a light novel that she herself would consider “the most interesting in the world” a title she believes Masamune’s work already deserves.

Muramasa is the author of The Legend of the Phantom Blade, a massively popular light novel series that outsells Elf Yamada’s work by over tenfold and has been adapted into anime twice. However, due to her reclusive nature and minimal involvement with the publishing company, she is unaware of the series’ full success. She lives on a modest monthly allowance of 4,500 yen and rarely visits the publisher’s office.

Despite the series’ success, its continuation has stalled. The primary reason is Muramasa’s frustration over Masamune’s decision to shift from writing battle-themed stories to romantic comedies. Many fans have noted the similarity in writing styles between the two authors, mistakenly assuming that Masamune is imitating her. In truth, Muramasa had long been inspired by Masamune’s work.

Roughly a year prior to the series’ events, Muramasa began writing stories with overlapping themes to Masamune’s, effectively derailing his plans and preventing him from releasing a book. While this is suspected to be intentional, no definitive proof has surfaced. Her social disinterest is further reflected in her refusal to attend year-end parties, award ceremonies, or other industry events.

Muramasa used her connections at the publishing house to obtain a copy of Masamune’s latest proposal. Upon discovering his change in genre, she was infuriated crumpling the proposal and discarding it in anger. To further express her opposition, she leveraged her influence to secure an earlier publication slot, thereby delaying Masamune’s manuscript release by a full year.

Masamune Izumi
Muramasa has long admired Masamune Izumi, having followed his work since his early days as a web novelist. Inspired by his writing, she decided to pursue a career as a novelist herself. When she discovered that Masamune had shifted genres from action-based stories to romantic comedies, she was deeply disheartened. Believing that battle-themed novels were his true strength, she attempted to sabotage the release of his new work not out of spite, but in hopes of rekindling his original creative passion.

Upon learning more about Masamune’s personal life and his financial struggles with his stepsister Sagiri, Muramasa offered him support, even suggesting that he work under her so she could assist him financially. She openly confessed her romantic feelings for him, but was ultimately rejected, an experience that mirrored Masamune’s own rejection by Sagiri. Despite this, Muramasa remains undeterred, continuing to cheer him on both as a devoted fan and a hopeful romantic interest.

Elf Yamada
Muramasa views Elf Yamada as a romantic rival for Masamune’s affections, and the two often clash. Due to her general indifference toward others in the light novel industry, Muramasa frequently forgets Elf’s name and has little respect for her writing, calling her books dull. Elf, in contrast, enjoys provoking Muramasa and teasing her whenever possible. Despite their rivalry, the two are capable of working together when their goals align, showing a pragmatic side to their dynamic.

Sagiri Izumi
Muramasa has limited interactions with Sagiri Izumi, also known as Eromanga Sensei. Their first notable encounter occurred when Sagiri left her room for the first time in the series to confront Muramasa, accusing her of trying to take Masamune away and abandon their shared dream. Muramasa also complied when Sagiri scolded her and Elf for creating a disturbance during a contest after-party. Though not much is known about her opinion of Sagiri, Muramasa appears to respect her on some level perhaps even viewing her as a quiet but significant presence in Masamune’s life.

Ayame Kagurazaka
Ayame Kagurazaka, an editor at Muramasa’s publishing house, plays a recurring but often overlooked role in her professional life. Muramasa rarely visits the publishing office and does not recall interacting with Kagurazaka frequently. However, Ayame attributes this to Muramasa’s reclusive tendencies. Despite the lack of recognition, Muramasa listens closely whenever Kagurazaka offers advice, particularly when the subject involves Masamune.