Osaka
Osaka is for travelers who find Tokyo polite to the point of reserve. The local motto, kuidaore, roughly "eat until you go broke," is taken seriously, and the city's old nickname, the nation's kitchen, dates to its role as Japan's rice-trading hub in the Edo period. Dotonbori's canal-side neon is touristy, but it is still the center of the city's street food, from takoyaki to okonomiyaki built from whatever fillings you choose.
Tokyo has far more neighborhoods and the bigger art and design scene. Osaka is louder, looser and within easy day-trip range of Kyoto and Nara by train.
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