This is exactly the kind of decision where "just book whatever's cheapest" quietly costs you either money or a whole day. Mio doesn't care about the romance of the journey — here's the math.
Each mode trades money for time differently. The Shinkansen is fast and predictable but expensive. An LCC (Peach, Jetstar) can be very cheap when booked weeks ahead with only a small bag — but the fare balloons if you add luggage, and you still lose time and money getting to and from airports. The overnight highway bus is usually the cheapest way to cover medium distances, and because you sleep on board you skip one night of lodging. The Seishun 18 Kippu gives you flat-price, unlimited local-train travel for a set number of days — brilliant per kilometre if you have time and no deadline.
| Mode | Rough cost | Time (door-ish) | Best for |
|---|---|---|---|
| Shinkansen | Highest | ~3 hours | You value time / have a fixed schedule |
| LCC (Peach / Jetstar) | Low if booked early + light bag | ~4–5 hours with airport access | Booked ahead, minimal luggage |
| Overnight highway bus | Usually cheapest | ~8 hours (you sleep) | Medium distance + saving a night's lodging |
| Seishun 18 Kippu (local trains) | Cheapest per-km on long trips | ~9+ hours, many changes | Unhurried long trips in season |
Notice the pattern: the two "cheapest" rows are also the two slowest. If a lost half-day would cost you more in work, plans, or exhaustion than the fare gap, the bus and the 18 Kippu stop being cheap.
The 18 Kippu is only sold and valid in fixed spring, summer, and winter windows tied to school holidays. Outside those windows you simply can't buy it — so it's a plan-ahead tool, not an any-day option. Within a window, it's a flat price for a set number of local/rapid-train days, which is why it wins per kilometre on long, patient journeys. It is not restricted by nationality: residents and tourists can both use it.
Smart middle path: if you're on a tight budget and travelling in season with time to spare, chain a couple of 18 Kippu days for a long trip; otherwise, an early-booked LCC or an overnight bus usually beats the Shinkansen on cost while costing you only a few hours.
Value your time first. If an hour of your day is worth a lot right now → Shinkansen or an early LCC. If it isn't, and you're not in a hurry → overnight bus for medium trips, or the Seishun 18 Kippu in season for long ones. The "cheapest" ticket is only cheap if the hours it costs are hours you were happy to spend.