Ataru's Mother, known only as Mrs. Moroboshi, is a central supporting character in the daily chaos of the Moroboshi household. Her background is that of a traditional, middle-class Japanese housewife, who likely expected a quiet, conventional life. Instead, she finds herself perpetually exasperated by her family, most notably her only son. Her days are spent managing the household, cooking, and engaging with neighbors, though her domestic peace is constantly shattered by the extraterrestrial and supernatural events her son attracts.

Her personality is defined by a sharp, high-strung, and often verbally harsh demeanor. She is quick to express her frustration and embarrassment over Ataru's lecherous, lazy, and troublesome nature. Her most famous lament is the wish that she "never should have had him," a statement she often makes directly to her son or to her husband, showcasing a form of verbal and emotional abuse, though this trait becomes less frequent in later stories. Despite her constant nagging and harsh words, a deep, if often hidden, love for her family exists. She becomes genuinely distraught at the thought of losing Ataru, revealing that beneath her complaints, she still sees him as her child. She bosses her timid, salaryman husband around frequently, creating a dynamic where she is the louder, more forceful presence in the home.

Mrs. Moroboshi's primary motivation is the pursuit of a normal, peaceful, and respectable life. She dreams of a quiet home and is deeply ashamed of Ataru for making her unpopular with the neighbors and for constantly putting their family in the center of bizarre incidents. Her actions are largely driven by a desire to maintain social standing and domestic tranquility. In the film Only You, this motivation extends to a pragmatic agenda; she joins forces with Lum's parents to force a marriage between Ataru and Lum, believing it will secure a better, more luxurious life for herself on Lum's homeworld.

In the story, her role is primarily that of the long-suffering parent and a voice of "normal" societal frustration amidst the absurdity. She represents the grounded, everyday world that is constantly upended by the alien chaos. She is not a driver of the main plots but a reactor to them, often providing a commentary of despair or annoyance. A key relationship is, of course, with Ataru. She showers him with verbal abuse and disappointment, yet her underlying maternal care surfaces in moments of genuine crisis. In stark contrast, she adores Lum, treating her like the daughter she always wished she had. She frequently showers Lum with more affection and praise than she ever gives Ataru, much to his chagrin. Her relationship with her husband is one of quiet co-dependence; while she nags and bosses him, he passively endures, and they share a mutual bond in their shared regret and affection for their son. In a rare moment of flighty behavior, she develops a short-lived crush on the handsome but simple-minded Rei, a boy her son's age, much to her husband's despair.

While she undergoes little fundamental development, there is a softening of her most vicious traits as the series progresses. Her catchphrase of wishing Ataru was never born appears less frequently in later chapters, suggesting a grudging acceptance of her chaotic life. Regarding notable abilities, Mrs. Moroboshi possesses no supernatural powers. Her most significant ability is her formidable endurance and mental fortitude. She is a "very strong woman," as one description notes, capable of taking care of a "useless husband and a good-for-nothing son" while withstanding the constant destruction of her home and the stress of her daily routines. Her strength is purely one of character, a resilience that allows her to keep the household running despite the ceaseless pandemonium.