Nenki-uri (whose "ki" can be written with three different characters 年期売, 年季売 or 年紀売, all of which relate to time or duration) was a kind of contract of sale (usually of land) used during Japan's medieval period. Under a nenki-uri contract, the thing being sold, be it land or something else, was sold to the buyer for a certain fixed interval in exchange for an agreed-upon price the seller would receive, and upon expiration of the length of time stipulated in the contract, the object would automatically revert to the control of the seller.
Since the actual documents of such contrasts became useless after their expiration, most of them were destroyed and consequently the surviving examples are very few, but it seems 10- or 20-year contracts were the most common, with a few examples of 30- or even 50-year contracts. It is believed that people would enter such contracts only after setting a sale price that included the anticipated earnings during the term of the contract from the thing being sold, as well as the corresponding interest from those earnings. Furthermore, most contracts had many provisos written into them that stipulated the wording of what constituted a crime or breach to ensure that if the buyer broke the agreement made with the buyer during the contract period, it would be recognized that the seller would immediately buy back whatever was sold, just as with a honsengaeshi (a land sale that had the seller buy the land back in such a situation; nenki-uri were also worded in such a way as to have sellers buy back whatever had been sold), and moreover, that the seller's obligations for labor (and the distribution of other assignments) as well as the collateral offered for the sale would be disposed of, and that those possessions which could be sold would be pawned.
Some seek to explain the roots of the nenki-uri contract as coming from the chinso (land tax) of ancient times, but the prevailing view is that the nenki-uri first came into existence during the Kamakura period. Medieval methods for selling land included the permanent sale, which corresponds to land sales today, the honsengaeshi, under which those with capital could buy back the sold land, and finally the nenki-uri, but it is thought that the nenki-uri, under which the seller had the most pronounced authority and power, became the most widely used contract, especially among farmers. And although with the advent of warrior society warriors were forbidden from permanently selling the lands from which they drew their stipends, some daimyo allowed the existence of laws within their own domains that permitted warriors to sell their land via nenki-uri under exceptional circumstances, in an attempt to provide financial relief for warriors in dire economic straits.
Moreover, though the Einin-era debt cancellation order does not include any provisions regarding nenki-uri, the debt cancellation orders given during the Kenmu Restoration and under the Muromachi bakufu (Japanese feudal government headed by a shogun) do explicitly apply to nenki-uri.