In Japan, the "best" size for a suitcase is a medium spinner (24–26 inches) or a standard carry-on. While you can technically bring a large 30-inch suitcase, it can be extremely difficult to navigate through crowded train stations, narrow sidewalks, and small hotel rooms. Furthermore, the Shinkansen (bullet train) has strict rules for "oversized" luggage: any bag where the total dimensions (height + width + depth) exceed 160 cm (63 inches) requires a specific "oversized baggage" seat reservation. If you board without this reservation, you may be charged a 1,000 Yen fine, and your bag might be moved to a different car. To avoid this hassle, many travelers use Japan's excellent Takuhaibin (luggage forwarding) services like Yamato Transport (the "Black Cat"). For about $15–$25 per bag, you can send your luggage from one hotel to the next, allowing you to travel light on the trains with just a small backpack. This is highly recommended because most local commuter trains and subways have very limited storage space, and dragging a massive suitcase during rush hour is considered a major social faux pas in Japanese culture.