Futaba Igarashi is a petite adult woman with a slender build, often mistaken for a child due to her small stature. She has shoulder-length green hair, which she typically ties into a ponytail, and forest-green eyes that complement her youthful appearance.

In the workplace, she wears a formal suit, adhering to professional attire. During colder seasons, she is frequently seen wearing a red muffler, adding a distinct touch to her otherwise standard office outfit.

Futaba Igarashi compensates for her petite stature by adopting a boisterous and outspoken demeanor, especially around her coworkers and family, who frequently treat her like a child despite knowing her actual age. She is highly expressive and easily flustered, often reacting strongly to teasing particularly from Harumi Takeda. Though she tends to be emotional, she makes a conscious effort to conceal her feelings, striving to maintain a sense of professionalism in the workplace. Despite her frustrations, she is hardworking and determined, always seeking to prove herself as a capable employee.

Futaba Igarashi’s relationship with her senpai, Harumi Takeda, is anything but simple. Their first meeting set the tone for their dynamic when Takeda mistook her for a middle-schooler on a field trip, much to her dismay. From that moment, everything about him became an annoyance, his over-familiarity, his loud and carefree personality, and his tendency to tease her. However, over time, her perception of him gradually began to change.

As Takeda took Igarashi under his wing, they spent most of their days together at the office and on sales calls, where he provided her with mentorship and support. Despite his teasing, he was always dependable and protective. Their relationship took an unexpected turn during a night of drinking when Igarashi, in a tipsy state, flirtatiously asked if Takeda liked her. He casually admitted that he did, though he framed it in an almost parental way, stating that if he were married and had a child, he would want them to be like her. This response frustrated Igarashi, prompting her to blurt out why she couldn’t be the wife in that scenario. Though Takeda brushed it off, the moment forced Igarashi to confront her feelings, whether she was ready to or not.

Throughout the manga and anime, Igarashi struggles with her emotions, torn between acknowledging her growing affection for Takeda and refusing to admit it outright. Their relationship gradually shifts beyond the typical senpai-kōhai (mentor-mentee) dynamic, evolving into a close friendship. They look after each other outside of work visiting when one falls ill, spending time together outside of the office, and even taking care of each other in personal situations.

Despite Igarashi’s denial and Takeda’s apparent obliviousness (or intentional restraint), those around them, Tōko Sakurai, Sōta Kazama, and Igarashi’s best friend, Natsumi Kurobe easily pick up on their chemistry. They subtly encourage Igarashi, whether it’s helping her pick out gifts for a “mystery” recipient or choosing an eye-catching swimsuit for their beach outings. Even Igarashi’s grandfather, fiercely protective of his granddaughter, is wary of Takeda’s presence in her life. However, after discovering their shared love for Igarashi, he gradually warms up to Takeda.

Despite these developments, Igarashi’s biggest struggle remains the same, she wants to be seen as an adult, not a child. Ironically, the only person who truly acknowledges her as a grown woman most of the time is Takeda. Their relationship remains in a delicate “will-they-or-won’t-they” state, as the series is still ongoing, leaving their romantic future uncertain.

Harumi Takeda
Takeda is Igarashi’s senior and mentor at work, for whom she develops a deep yet conflicted affection. While Takeda enjoys teasing Igarashi about her height and demeanor, he nonetheless recognizes her as a competent colleague and treats her as an adult, even if he rarely admits it to her directly. Despite their frequent bickering, Takeda is always dependable, providing guidance and support both professionally and personally. Their relationship remains ambiguous, with Igarashi struggling to acknowledge her feelings while Takeda’s true thoughts remain unclear.

Sōta Kazama
Kazama is Igarashi’s coworker and senior, known for his reserved and observant nature. Unlike Tōko Sakurai and Natsumi Kurobe, he does not actively tease Igarashi about her relationship with Takeda. However, he clearly notices their connection and occasionally provides quiet support, choosing to observe rather than interfere.

Tōko Sakurai
Sakurai, another senior employee, recognized Igarashi’s feelings for Takeda before even Igarashi herself. She takes pleasure in teasing Igarashi about her obvious crush, often nudging her toward recognizing and acting on her emotions. Despite this, Sakurai remains a supportive and well-meaning friend.

Natsumi Kurobe
Kurobe is Igarashi’s former high school classmate and close friend. The two share a strong bond, though Igarashi occasionally feels jealous of Kurobe’s figure in comparison to her own petite frame. Their friendship is marked by playful banter and mutual support. It is heavily implied in My Senpai is Annoying Vol. 9 that Kurobe may have had a crush on Igarashi at some point.

Futaba’s Grandpa
Igarashi’s grandfather is the only known living relative mentioned in the series, aside from her deceased grandmother. While they share a close relationship, his overprotectiveness frequently frustrates her, as he refuses to see her as an adult. He takes an immediate disliking to Takeda, viewing him as an intruder in his granddaughter’s life. This has led to multiple confrontations between the two, though over time, he begins to acknowledge Takeda’s genuine care for Futaba, albeit begrudgingly.

The name Futaba (双葉) is composed of “futa” (双), meaning “pair” or “set,” and “ha/ba” (葉), which can mean “leaf, plane, lobe, needle, blade, spear, counter for flat things, fragment, or piece.” Together, Futaba (双葉) literally translates to “bud, sprout, or twin leaf,” symbolizing growth and new beginnings.

Her surname, Igarashi (五十嵐), is written with “ig” (五十), meaning “fifty,” and “arashi” (嵐), which means “storm” or “tempest.” The combination gives a strong and dynamic impression, possibly reflecting her energetic and outspoken personality.