I tried the most expensive cabin, First Class Royal, on the ferry from Osaka to Ehime Japan. If you are looking for a big private cabin and a short ferry trip, this might be a good option.

There are four Royal Cabins on this ferry (two twins and two doubles).
The fare was 25,650 JPY / 233 USD.
One adult is 17,100 JPY. Two adults are 34,200 JPY. If you book a Royal Cabin alone, you need to pay extra 50% of one adult fare (8,550 JPY).

17,100+8,550=25,650

*Above fares are calculated on the B period. (There are A, B, C in a year)
*The fare changes depending on the season

The ferry is operated by Orange Ferry

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