A term appearing in the Tsukumogami Emaki, an otogizōshi picture scroll from the sixteenth century. The introduction to the scroll states that:

陰陽雑記云器物百年を経て化して精霊を得てよく人を訛かす是を付喪神と号といへり
According to the Onmyō Zakki, vessels pass their hundredth year, transform, obtain a soul, often bewitch humans, and are called tsukumogami.

The scroll goes on to tell the story of a group of old household objects that have been discarded on susuharai (end-of-the-year housecleaning). Having obtained sentience, the centenarian objects discuss with one another their offense at having been thanklessly thrown away after their long period of service. In their rage, they express a desire to become monsters and have their revenge, but a Buddhist rosary named Ichiren Nyūdō objects and asks his fellow tools to view their fate as simple karma. The hand-pole Aratarō, having none of this, beats the rosary until his clasp breaks. Ichiren flees for his life.

Now the old scroll Master Kobun teaches the other artifacts the secret art of transforming, as taken from the Onmyōdō theory of yin and yang. They must wait for Setsubun, when yin and yang change places, and "throw away" their lives so that the Deity of Creation, who oversees the shaping of all things, will remake them with new and monstrous bodies. Following these instructions, the objects soon take a variety of new shapes. Now that they can properly avenge themselves, they begin devouring people and livestock and terrifying the populace. Elated at their success, the new monsters throw parties, compose poems, and enshrine and devoutly worship the Deity of Creation.

They continue in this fashion until they have a chance encounter with the chief advisor to the emperor, who happens to be carrying a powerful charm. It calls forth a halo of flame which sends the fiends running for their lives. From here the tsukumogami's luck only worsens - the emperor now has the priest who made the advisor's charm perform his prayers, an act which summons several gohō-dōji (divine boys in the service of Fudō Myō-ō). The powerful spirit children seek out the monsters' home and defeat them with ease.

Soundly beaten, the tsukumogami decide to accept the error of their ways and convert to Buddhism. They seek out old Ichiren, who has withdrawn from the world and lives in hermitage in the mountains. Ichiren forgives his old friends, and instructs them in the Shingon sect of Buddhism, which he believes is the speediest path to Nirvana. In this fashion all the old tools, though once only inanimate objects, swiftly attain enlightenment and become Buddhas. ^1,2,3

Though the word tsukumogami is not often found in surviving pre-modern sources, the basic idea of inanimate objects transforming into animate ones after becoming very old has long been common in Japan. ¹ Object-monsters appear frequently in folklore and art, and make up many of the creatures in the famous Shinju-an Hyakki Yakō Emaki 真珠庵百鬼夜行絵巻　of the Muromachi period and the numerous picture scrolls of the same genre. ⁴

In addition, the word tsukumogami seems related to another word pronounced the same way, written 九十九髪 (hair of ninety-nine) and referring to an aged person's white hair. The connection is obvious in that both words allude to a lifespan of a hundred years, so perhaps the two are the result of a pun or a divergent writing.⁵


Additional Sources
1. Lillehoj, Elizabeth. "Transfiguration: Man-made Objects as Demons in Japanese Scrolls." Asian Folklore Studies 54:1 (1995): pp. 7-34.

Citations
1. Murakami 2005 p. 212.
2. Lillehoj pp. 21-2.
3. “Tsukumogami (Synopsis).” Enjoying Otogi Zoshi. 2003. Kyoto University Library. 8 Mar. 2009 .
4. Lillehoj p. 8-9.
5. Lillehoj p. 28-9.