“Are you listening?” Kazu continued. “When you return to the past, you must drink the entire cup before the coffee goes cold.”“Uh. I don’t actually like coffee that much.”Kazu opened her eyes wider and brought her face an inch or so from the tip of Fumiko’s nose.“This is the one rule you have to absolutely obey, ” she said in a low voice.“Really?”“If you don’t, something terrible will happen to you . . .”“Are you listening?” Kazu continued. “When you return to the past, you must drink the entire cup before the coffee goes cold.”“Uh. I don’t actually like coffee that much.”Kazu opened her eyes wider and brought her face an inch or so from the tip of Fumiko’s nose.“This is the one rule you have to absolutely obey, ” she said in a low voice.“Really?”“If you don’t, something terrible will happen to you . . .”