"Uchū Ichi no Musekinin Otoko" centers on the life of Tetsuro Hoshino, a young orphan living in a dystopian future where humanity has colonized the stars but remains plagued by inequality and corruption. Tetsuro's journey begins when he encounters Captain Harlock, a legendary space pirate known for his rebellious spirit and unwavering sense of justice. Harlock becomes a mentor figure to Tetsuro, guiding him through the perils of space and teaching him the values of freedom and responsibility.

The narrative unfolds as Tetsuro and Harlock embark on a quest to find the mysterious planet Arcadia, a mythical place said to hold the key to humanity's salvation. Along the way, they face numerous adversaries, including the oppressive Earth government and its military forces, which seek to maintain control over the galaxy. The story explores themes of rebellion, loyalty, and the struggle against tyranny, as Tetsuro grows from a naive boy into a determined and capable individual.

Key characters include Captain Harlock, whose enigmatic past and unyielding principles drive much of the plot; Tochiro Oyama, Harlock's close friend and the genius behind the advanced technology of their ship, the Arcadia; and Emeraldas, a fierce and independent space captain who shares a complex history with Harlock. The interactions between these characters add depth to the story, highlighting their shared ideals and personal conflicts.

The manga blends action, adventure, and philosophical undertones, presenting a richly detailed universe filled with space battles, political intrigue, and moral dilemmas. The plot is driven by the characters' pursuit of freedom and their resistance against oppressive forces, culminating in a climactic confrontation that challenges their beliefs and resolves their personal arcs. Through its exploration of human resilience and the quest for meaning, "Uchū Ichi no Musekinin Otoko" offers a compelling narrative that resonates with themes of hope and defiance.