Smart cards like Icoca, Suica and Pasmo are generally valid across Japan, so don't worry about which one you buy. You can use Icoca/Pasmo/Suica for all trains, subways and buses in Osaka. You can also use Icoca/Pasmo/Suica at many shops, especially convenience stores.

Yes, you can absolutely use a Welcome Suica card in Osaka in 2026. While Suica is a product of JR East (based in Tokyo), it is part of the nationwide interoperable IC card network. This means it works seamlessly on virtually all subways, buses, and private railways in Osaka and the surrounding Kansai region, just like the local "ICOCA" card. You can also use it at convenience stores, vending machines, and many restaurants in Osaka. However, there are two major caveats to keep in mind: first, the Welcome Suica is valid only for 28 days from its first use, after which it becomes void and any remaining balance is lost. Second, you cannot get a refund for any unused balance on a Welcome Suica card, nor can you return it in Osaka; if you have money left on it, you should spend it at an airport shop before leaving Japan. For a trip that starts in Tokyo and ends in Osaka, the Welcome Suica is incredibly convenient, but you must manage your balance carefully to ensure it reaches zero before the 28-day expiration.