Dr. Inoue presents the three siblings with the 500 Million Year Button, an offer of one million yen in exchange for pressing it. The one who presses the button must endure 500 million years of solitude in an empty, timeless void. When the time has passed, their memory of the experience is erased and they return to the exact moment the button was pressed. He extends this offer while the siblings' father lies critically ill and the family struggles under the weight of mounting medical bills.