We couldn't believe the boarding price. It was only 150 yen.

This is the ferry you take to access Onomichi. If you don't take this ferry, you have to loop around so it is highly recommended. Likewise if you are going from Onomichi to the islands.

About:

The boarding area for Tsuchidō run by Onomichi Watashibune is a small, no-frills quay near the main harbor where you should arrive about 10 minutes before departure so you can line up and stow any bags. Tickets are often bought at a small counter or directly from the crew when you board, so bring cash and a few coins in case card machines are not available. Signage and English may be limited, so look for the company name on the boat and ask staff if you are unsure; the crossing is short, so luggage space is minimal and accessibility can be tight. Check the timetable in advance since services can be infrequent in the evening and off-season, and be prepared for basic shelter only while you wait.