Yes, you can board most Shinkansen trains without a reservation by purchasing a Non-Reserved (Jiyu-seki) ticket. These tickets are typically cheaper than reserved ones and allow you to sit in specific designated cars (usually cars 1–3). However, you are not guaranteed a seat; if the train is crowded, you may have to stand in the aisle or the vestibule area. It is important to note that certain high-speed services, such as the Hayabusa (Tohoku line) and Kagayaki (Hokuriku line), are "All-Reserved," meaning you must have a seat assignment to board. Furthermore, during peak holiday periods—specifically the New Year (late Dec to early Jan), Golden Week (early May), and Obon (August)—popular trains like the Nozomi often switch to an "All-Reserved" status to manage extreme congestion. In 2026, it is highly recommended to check the seasonal schedule on the SmartEX app or at a JR ticket office before traveling to ensure your desired train offers non-reserved seating.