Heh, Yukari is precognitively quoting Spider Robinson.
It's interesting that only the "Summer" story isn't about clutching at human warmth despite asynchronous lifespans. Immortality is a bitch.
(Yuyuko and Yukari have a terribly tragic backstory, but Moukou and Kaguya have the most terribly tragic inevitable future story. When humanity dies out, they'll still be here. When the sun swallows the earth, they'll still be here. When entropy inexorably grinds all things to the heat death of the universe, the whole of the cosmos a flat near-vacuum at 5°K, they'll still be here.)
