Visas
Japan allows short-term visa-free entry for tourism to a long list of nationalities, but the exact rules, allowed stay length and any pre-registration requirements vary by passport and do change from time to time. Check your own country's current requirement against Japan's official immigration guidance a few weeks before you fly, rather than relying on what a friend's trip required last year.
Cash still matters
Card and contactless payment acceptance has grown a lot in Osaka, especially at chain stores, department stores and hotels, but plenty of smaller restaurants, market stalls and older shops remain cash-only or cash-preferred. Convenience store ATMs — 7-Eleven's in particular — reliably accept foreign cards around the clock, and are usually the easiest way to withdraw yen once you're on the ground.
Tipping isn't expected
Tipping isn't part of the culture anywhere in Japan, including restaurants, taxis and hotels, and attempting to leave one can sometimes cause more confusion than goodwill. Good service is simply the standard, not something tipped for separately.
Getting online
Airport counters and lockers at KIX offer both physical SIM cards and pocket wifi rental for pickup on arrival and drop-off before departure, and both are worth arranging in advance online rather than queueing to sort out jet-lagged. Free wifi is increasingly common in stations and convenience stores but is inconsistent enough that it shouldn't be your only plan.
Suica, Pasmo and ICOCA IC cards can now also be added to many phones' digital wallets before you even leave home, letting you tap into Osaka's trains the moment you land without a station queue.