"5-Oku-Nen Button" is a science fiction manga series that explores themes of time, mortality, and the consequences of human choices. The narrative centers on a mysterious button that grants its user the ability to travel 500 million years into the future. The protagonist, a young man named Takumi, stumbles upon this button during a moment of personal despair. Intrigued by its potential, he presses it, only to find himself transported to a distant future where humanity no longer exists, and Earth has undergone drastic environmental and geological transformations.

The story delves into Takumi's experiences in this alien future, where he encounters remnants of advanced civilizations and struggles to comprehend the vastness of time. The button's mechanism allows him to return to his original timeline, but each use comes with a cost: the irreversible passage of time in his own life. As Takumi grapples with the implications of his actions, he begins to question the value of his existence and the fleeting nature of human life in the grand scope of the universe.

Supporting characters include Takumi's friends and family, who remain unaware of his time-traveling abilities but are affected by his increasingly distant behavior. The narrative also introduces enigmatic figures from the future, who provide cryptic insights into the button's origins and its purpose. These interactions deepen the philosophical undertones of the story, as Takumi confronts the ethical dilemmas of altering time and the inevitability of entropy.

The plot unfolds through a series of episodic adventures, each exploring different facets of the future world and the emotional toll of Takumi's journey. Themes of isolation, existential dread, and the search for meaning are interwoven with moments of wonder and discovery. The manga's pacing balances introspective character development with speculative science fiction, creating a thought-provoking exploration of humanity's place in the cosmos.