Although this 'secret box' was stolen by the Shimazu clan and it is not known what the box contained, it is considered that the box might have contained a sacred sword (one of the San-shu no jingi), which was otherwise believed to have been lost at sea during the Battle of Dannoura.
この「あかずの箱」というものは、中身未確認のまま島津氏に奪われたが、この箱の中には、三種の神器のうち、壇ノ浦の戦いで海底に沈んだとされる宝剣が入っていたのではないかと考えられる。