Dr. Hanamaru recurs as a scientist character across multiple early science fiction works. His visual design includes distinctive abundant white whiskers, a kindly facial expression, and a potbelly. He consistently functions as a benevolent narrative figure, often serving as a prologue narrator or exposition provider. His characterization remains uniformly good-natured across all appearances, with no instances of villainy or moral corruption.

Within the "Big X" narrative, he participates under duress in the Nazi research project developing the weapon "Big X" for Hitler during World War II. Concerned about the weapon's destructive potential, he deliberately delays the research, cautiously collaborating with the morally ambiguous co-researcher Dr. Engel. His resistance leads to execution by German forces shortly before Germany's defeat. Before his death, he conceals critical information by implanting a card containing the weapon's secrets into his son, Shigeru, enabling future resistance against its misuse.

Beyond "Big X," the character appears extensively in other productions. His roles vary but consistently feature his profession and benevolent demeanor. These include portrayals as a university professor in "Astro Boy /Adventure on Mars," a minister in "The Plain of Abusegahara" and "Strange Travel of Dr. Tiger," an art dealer in "The Pink Angel," a clergyman in "The Earth War," and various medical professionals in multiple "Black Jack" stories. These appearances span from 1948 to 1981.

Across official media, Dr. Hanamaru exhibits no significant character development or background expansion beyond these established parameters. His personality and narrative function maintain consistency, emphasizing reliability and moral integrity without substantive evolution or detailed personal history exploration.