The Mitsu-ishi Rock is a giant rock located in Nippo-Kaigan Quasi National Park lying along the coastline of Oita and Miyazaki prefectures. The name “Nippo” is the on-yomi reading of the combined first Kanji characters of two ancient province names; Hyuga Province (presently Miyazaki Pref.) and Bungo Province (presently Oita Pref.). This quasi national park, which was designated in 1974, covers the huge area from Sagaseki Peninsula in the north to Mimitsu area in the south. The coastline consists of rias. The sea in this area is known for fishing grounds of famous Seki saba, Seki aji, and Usuki fugu (blowfish). Because of the Kuroshio Current flowing along the coastline, the sea water is warm and has high transparency, so there are several marine parks. The area, called “Yabakei of the Sea,” has a lot of scenic spots with towering strange-shaped rocks including this Mitsuishi Rock and Meoto-iwa Rocks (wedded rocks), which is famous for being tied with Shimenawa (enclosing rope).