Exiting the Nanboku subway's Korakuen Station near Tokyo Dome, I gaze up at clouds resembling bunches of purple hydrangeas. Directly overhead, a roller coaster car swooshes by, its passengers shrieking, which is a good sign, because, despite its aquatic name, the Thunder Dolphin coaster doesn't run in rainy weather. Optimistic, I head west along Metropolitan Road 434, into the Koishikawa neighborhood.