Umaru Doma

The main character of this work. A year before the start of the story, she began living with her brother Taihei in Apartment 201 of "Koupo Yoshida." She is referred to as "Umaru" in the series. She has long ashen hair, celebrates her birthday on September 26, and her height varies between 40 cm in her "lazy sister" form and 160 cm as her "perfect sister" or UMR persona. Her blood type is AB.

Umaru attends the prestigious Araiyada High School, where she is admired for her beauty, excellent grades, and outstanding sports performance. Teachers often praise her, and she is popular across all age groups. However, her true nature is revealed at home, where she transforms into a "lazy sister" who prefers a slothful lifestyle, staying up late, and having an unhealthy diet. This transformation is not just psychological; it is perceived as a complete change in appearance by others like Kirie, making her look like an entirely different person. Her home appearance is a secret to all but Taihei and his colleagues Bomber, Alex, and Kanau’s sister Hikari. When Kirie saw her in her lazy sister form, Umaru pretended to be her own younger sister, "Komaru." Umaru emits a unique sound, "Umaruun," when she switches between her perfect and lazy sister forms or when her charming traits are highlighted.

In her lazy sister form, Umaru is referred to as "Master" by Kirie, "Tanukichi" by Bomber, and "Sensei" by Alex. No one apart from Taihei and Hikari realizes that the lazy Umaru and the usual Umaru are the same person. Occasionally, she throws tantrums, turning into her lazy sister form in front of Ebina, or attempts to tell Kirie the truth herself, but every character has their own secrets, resulting in no one noticing or talking about Umaru's double life.

Umaru keeps two hamsters and frequently lounges at home wearing an orange hoodie that resembles a hamster, paired with a plain white inner shirt and red shorts. She appears disinterested in fashion, possessing few outdoor clothes but multiple hamster hoodies. She has a distinct laugh that goes "nuehe," "nuhoho," or "nuffufu." She wears black knee-high socks with her school uniform or shorts.

Her favorite foods include soda, junk food, and meats such as hamburg steak. She especially loves soda, to the extent that she will go to a nearby convenience store to restock despite her dislike of going out. Ramen is also a favorite, although cup noodles are banned by Taihei. She dislikes vegetables and wasabi but can handle spicy foods with chili peppers. Umaru once made special "Kaki no Tane Chocolate" for Valentine's Day but generally has poor cooking skills. Though not as much as Ebina, Umaru has a considerable appetite.

Umaru is an avid reader of the manga magazine "Jumpu," with "Jumpiece" being her favorite. She tells her classmates that she doesn't read much manga at home due to restrictions and finds the reindeer character in "Jumpiece" cute.

Beyond manga, her hobbies include internet surfing, watching anime, and playing online games, often compounding into sleepless nights. She is highly skilled at gaming, excelling across various genres from console to arcade games. Disguised as "UMR" for incognito outings at game centers or subculture events, she is known as a prodigious gamer at the arcade GAPCOM (a real location called LION), regarded by staff as a genius marked by her eerie attire and game-crushing aura, though she is dismally poor at rock-paper-scissors.

While elegant outside, Umaru has a laid-back attitude at home, revealing a slightly cowardly, lonely side. She struggles to start conversations and often cries when Taihei scolds her. Despite her flaws, she has a genuine kindness, evident in her courteous behavior and occasional care for Taihei, who often doesn't notice due to her usual antics. Umaru is terrified of occult phenomena and ghosts, unable to watch horror movies alone, though she enjoys horror games.

Umaru adopts different personas based on her company: "Lazy Sister Umaru" at home or with Kirie and Hikari, "Perfect Sister Umaru" when with Ebina or the four friends, and "UMR" with Sylphynford.

She constantly imposes her whims on Taihei, sometimes exploiting him for her desires but often failing due to clumsy excuses. Her behavior stems from a deep trust and love for her dependable and kind big brother. For similar reasons, she harbors complex feelings towards the Kongou sisters.

As the story progresses, the distinctions between her personas blur, with more casual speech and outdoor hoodie-wearing becoming prominent. Taihei notes the increasing "ambiguity" in her roles. While Ebina, unaware of her secret, finds her easier to talk to.

By chapter 216 of volume 12, it’s revealed that her original, quiet personality (similar to her "Perfect Sister Umaru" appearance) was played up to converse more easily with her estranged brother. Hikari speculates that this acted persona might have become her main identity.

In the spin-off "Akita Imouto! Ebina-chan," it is revealed that Umaru and Ebina once met on a school event day. Ebina mentions a beautiful sister, but Umaru herself does not appear then.

Despite being one character, CD covers often depict her "Perfect Sister" and "Lazy Sister" forms together, suggesting a sisterly relationship.

In "character popularity polls," "Lazy Sister Umaru" ranks 5th, "Perfect Sister Umaru" 6th, and "UMR" 8th.