Many players have tried to reach the Coast of Oshima, but it is impossible to do so because the area is tied to the main quest. You must follow all the objectives of the main mission to unlock the new region. Here are all the details you must know to unlock Oshima Coast in Ghost of Yotei.
Enter The Gatehouse To Coast of Oshima In Ghost of Yotei

Oshima Coast unlocks during the Saito Brothers’ main quest. But it has a few requirements as well. You must complete the Kitsune and Oni main quest. In short, you must eliminate the Oni, the Kitsune, and the Saito Brothers before you gain access to the Oshima Coast.
The Saito Brother quest takes place in the Teshio Ridge. You will get the quest during the Yotai Six – Main Tale 5 quest. It will take some time to get the next one, as you will have to interrogate civilians or bounty hunters in Yotei Grasslands. Since the mission is designed in this manner, you will have no problem finding enemies and bounty hunters.
Then you will have the option to select the specific main tale information, pick the Saito Brothers. Your next objective is to find Master Yoshida’s Dojo near the Horosaru Falls. Get to the location, and you will soon get to train with him. The training session will help you learn various moves using the Odachi weapon.
The next set of objectives will be following Master Yoshida and eliminating Saito’s enemy forces. At the end, you will unlock the Odachi weapon permanently in your weapon arsenal and the next objective on the Saito Brother questline, “Meet Jubei and Oyuki at the Oshima Coast Gatehouse.”
Once you get to the gatehouse, you will only meet Oyuki, follow the next set of objectives until you rescue Jubei. You will eventually get the objective Enter the Gatehouse. Follow the objective, and you will unlock a new ranged weapon, Tanegashima. After the battle against the Saito’s forces, you will escape the fort and unlock the Oshima Coast.
Then you have to reach the Benten Port to continue with the rest of the Saito Brothers in Ghost of Yotei. This then also opens up the route for various collectibles and armor sets in this region, like the Nine Tails puzzle, Dueling Trees, and more.

