After losing his parents at a young age, Takami Akitoshi shares a quiet home with his elegant older sister Hitomi. His ordinary days end abruptly when a mysterious girl named Mina appears in his room, declaring herself Death and announcing that his lifespan has run out. Hitomi bursts in after hearing his cries and pleads for Mina to spare him, prompting the visitor to offer one chance at survival: if Takami fathers a child within a week, she will grant him another ten years. He turns toward Hitomi, the weight of the proposal settling between them.
