Certificate of Ownership (安堵状)
Certificate of ownership refers to the letter in which lords such as shogun, provincial military governor and feudal lord gave vassal samurais a guarantee for the ownership of a territory and enfeoffment from the Kamakura period onwards.
Summary
Given their nature, many of these letters have been well preserved; descendants of the original recipients have treasured them when they came into their possession and passed them on for posterity.
This kind of letters are very important historical materials because they allow us to detect brushstrokes and habits of feudal lords and others.