Suneko, a 17-year-old with striking blue hair, is the eldest of three siblings confronting a harrowing choice: press a button to secure a million yen for their father’s life-saving treatment but endure 500 million years of solitary confinement in a void, her memory of the ordeal erased upon return. Her decision anchors the narrative’s exploration of ethics and sacrifice, contrasting immediate familial salvation against the psychological toll of an unfathomable temporal abyss. Alongside her siblings, she weighs the visceral fear of endless isolation against the desperation to save their father, each grappling with the moral weight of trading unseen suffering for tangible hope. The story dissects their individual struggles, probing how each processes the collision of duty, guilt, and existential dread inherent in the button’s offer.