Hatabou debuted as a recurring character in *Osomatsu-kun*, created by Akatsuka's assistant Kenichiro Takai to broaden the manga's cast. His name, meaning "flag boy," was selected via a *Shonen Sunday* reader poll. He usually appeared younger than the Matsuno sextuplets, though sometimes shared their age or grade. Visually, he sported a removable Hinomaru flag protruding from his skull, shaggy kappa-like bowlcut hair, a single bucktooth, and distinctive vertical lines under his nose signifying a runny nose; early manga versions occasionally showed the flag emerging from his ears or omitted it entirely. Personality-wise, he often exhibited simple-mindedness and a free-spirited nature, frequently falling victim to bullying by characters like the sextuplets or Chibita. Yet some stories depicted surprising strength or cunning, showing him commanding subordinates for personal gain. His speech included the tic "da jo" or "jo," typically introducing himself with "Hatabō da jo!"

In *Osomatsu-san*, Hatabou appears as an adult roughly the same age as the Matsuno brothers but retains a significantly smaller stature, showing minimal growth from his teens. He wears green overalls over a light yellow hoodie. He maintains childlike qualities such as riding a tricycle and seeking friendships, often displaying simple-mindedness and kindness. However, early Season 1 portrayals revealed unsettling traits. As "Mr. Flag," he became a wealthy CEO but proved incompetent at managing finances and operations, leading his employees to abandon him after his fortune collapsed. His darker side emerged in "Tell Us, Hatabo," where, facing an employee revolt over his perceived uselessness, he retaliated by selling "mystery meat" via mobile vendors, suggestively sourced from those disloyal employees. This menacing characterization lessened after Season 1, with later depictions emphasizing innocence and vulnerability.

His relationships shifted across media. In *Osomatsu-kun*, his dynamic with Chibita fluctuated between friendship, mentorship, subservience, and outright rivalry, notably in the "Joe Hatabō" assassin persona storyline. Iyami often targeted him alongside other children. Dekapan occasionally served as a father figure or mentor, especially in the 1988 anime. In *Osomatsu-san*, these connections became less prominent, though he interacted socially with the Matsuno brothers, such as inviting them to his lavish birthday party or attending a high school reunion with them in the 2019 film, observing peers who had transitioned into conventional adulthood.

Alternate universe iterations included an American version with a U.S. flag, the pirate-themed "Joe Hatabō" with a skull-and-crossbones flag, and a communist iteration in the spin-off *Hatabō and Wanpei* published in *Akahata (Red Flag)*, featuring a solid red flag. A hypothetical future in a beer advertisement depicted him as a wealthy comedic actor with a nose hair mustache, attended by fans like Dayōn.