Muramasa Senju, whose real name is Hana Umezono, is a light novel author and a supporting character in Eromanga Sensei. She is a middle school student who uses the pen name Muramasa Senju. In public, she speaks in an old-fashioned, masculine tone and carries herself with a formal, serious demeanor, but in private she reveals a more childish and endearing side. She is almost always seen wearing a kimono, regardless of the setting.

Muramasa is a phenomenally successful writer, with her light novel series selling over fourteen million copies. Despite this fame and fortune, she shows little interest in public recognition or monetary gain. Her motivation for writing stems from a personal desire: she began creating stories because she could not find any novels that satisfied her own tastes. She is left-handed and prefers composing her manuscripts by hand rather than using a computer.

Her role in the story is that of a rival and later a romantic interest to the protagonist, Masamune Izumi. Initially, she appears to be an antagonist who looks down on Masamune and seems to challenge him professionally. However, it is later revealed that she has been his most devoted fan since his early web novel days. She was inspired by his series The Silver Wolf’s Reincarnation and began writing her own battle-heavy novels while waiting for his next volume. Her apparent hostility was actually a calculated effort to motivate him and reignite his passion for writing after he ended that series.

Muramasa’s key relationships include a deep admiration for Masamune, which eventually develops into a romantic crush. This puts her in a light rivalry with Masamune’s stepsister, Sagiri Izumi, who is also romantically interested in him. She also interacts frequently with fellow author Elf Yamada, and the two share a competitive but friendly dynamic. At school, Muramasa is well-liked by her classmates and is revered by members of the literature club, showing a social side that surprises those who only know her through her work.

Over the course of the series, Muramasa undergoes noticeable development. She learns to open up more to others, becomes more willing to participate in group activities, and acknowledges her feelings for Masamune. Her notable abilities include being a once-in-a-generation literary prodigy, capable of writing highly popular school battle stories at a young age. She is also recognized as one of the eight Hachiraijin—top-selling novelists who have sold over ten million copies each.