While the Suica card is remarkably versatile across Japan, it has specific limitations. Primarily, it cannot be used for continuous travel between different IC card regions; for example, you cannot tap in at a station in the Tokyo (JR East) area and tap out in the Sendai or Niigata areas. You must exit and re-enter. It is also not valid on Shinkansen (bullet trains) unless you have specifically linked it to the "SmartEX" or "JR-East Train Reservation" system beforehand. Additionally, Suica is generally not accepted on long-distance highway buses, at most traditional ryokans, or at very small, rural stations that lack IC readers. Some specific systems, like the PiTaPa area in the Kansai region (Osaka/Kyoto), may accept Suica for transport but not for specialized "PiTaPa-only" retail discounts.