彼岸の対義語は此岸(しがん) https://www.ryoegami.com/blog/%e5%bd%bc%e5%b2%b8%e3%81%ae%e5%af%be%e7%be%a9%e8%aa%9e%e3%81%af%e6%ad%a4%e5%b2%b8%ef%bc%88%e3%81%97%e3%81%8c%e3%82%93%ef%bc%89/