Ichinomiya Nagatsune was born in Kyoho 6 (1721) at Tsuruga in and was called Kashiwaya Chuhachi. He began as a gilder, then went up to Kyoto to become a metal carver and studied under Yasui Takanaga, a craftsman of the Goto line. He signed first Setsuzan, later took the name Nagatsune, and used the art name Ganshoshi, among others. He also studied painting under Ishida Yutei, the teacher of Maruyama Okyo, and the published sources hold that he was accomplished as a painter in his own right, as his surviving design-books show. In Meiwa 7 (1770), at fifty, he received the title -daijo, later changed to -no-kami, and he died in Tenmei 6 (1786) at sixty-six. The 's commentary repeats two verdicts on almost every piece: that he was praised as "Somin in the East, Nagatsune in the West", and that he is counted with Tetsugendo Shoraku and Otsuki Mitsuoki among the Three Masters of Kyoto metalwork.
The same commentary defines his hand in one sentence: he was skilled in the high relief of the Goto manner as well, but it was flat inlay with single-cut chiselling that made his name. in gold, silver, and is set flush into a polished plate, and the drawing is cut over it in katakiri-bori. On a Budai and Chinese children the published sources describe the chisel running from strong, deep strokes to the finest light touches, a katakiri-bori free in depth "that truly only Nagatsune could achieve". On a of Guan Yu they note the precise inlay of the coloured metals and a line ranging from the strong, deep outline to the fine work of beard and robe, and call the whole "truly in the Nagatsune manner". His painting study shows in the drawing itself. A painters' dictionary of 1927, cited by the , records that he liked to sketch bamboo shoots, horsetails, snails and frogs from life and astonished those who saw them.
That drawing from life is most evident in his animals. Of a with a stream full of turtles, carved in high relief in gold, and copper over a polished plate, the commentary writes that his carving of small creatures is, as one would expect, the work of genius. A pair of turtle is carved down the sides and even under the head, so that the animals seem alive and moving. A toad is caught at the instant before it springs, a snail renders the peculiar texture of the skin and the glossy volume of the shell, and in a gold of a tigress and cub the curve from the mother's shoulder along the back to the tail is called a form peculiar to Nagatsune. On he often changes the metal between the two pieces, gold against or against in the day-and-night manner. His dragon in solid gold is said to differ in spirit from the house-carved dragon of the Goto, with a new and free composition. A recurring point in the commentary is that his designs do not stop at the face of the piece. On and the picture continues over the back edge, the rim or onto the reverse, and the calls this one of the things to look for in his work.
The published sources name Setsuzan as his former name, and four so signed show the early hand. One is of iron, with the Rashomon and the demon Ibaraki-doji in high relief, and three are of brass with a -kusarashi finish: two of the archer Yuki shooting down a small bird from horseback, and one of lions set across front and back. Here the carving is called bold and vigorous, high relief combined with shishiai-bori to deepen the perspective, and the lion is described as a fine piece of the Setsuzan period with a vivid realism. The mature signatures follow his rank: Nagatsune with his , Ganshoshi Nagatsune, -daijo Nagatsune and -daijo Minamoto Nagatsune, with paired signed in split form across the two pieces. A of mandarin ducks under snow-laden willow is signed at the age of sixty-five; he died the following year at sixty-six. It is a full work in layered high relief, and its chisel, the commentary says, has a force hard to believe of his very last years. Two stand outside his usual manner, high relief and colour on after the Namban style: the Four Divine Beasts signed with the added words "carved at leisure", and a pair of dragons signed "carved in jest after drinking".
The records that are his most numerous works, followed by , and , and that his are very few. His work is set beside, rather than within, the house carving he learned. A of the treasures with Daikoku is called a fine piece showing the Goto manner, and the of the Three Laughers and of the mandarin ducks are likewise high relief in colour on . Against that, the and in flat inlay and katakiri-bori are the work for which the published sources call him "Nagatsune of the West". The commentary does not name his pupils. One of Guan Yu is recorded in his own book of carving designs.
Nagatsune's designated record is thirty-seven works: thirty-six at the rank and one of the Three Laughers of Tiger Ravine, certified in 24 (1949) when it was owned by Miyazaki Tomijiro. Twelve are , twelve are pairs of and eleven are , and two are , one of them a pair. He has no pieces, no Important Cultural Properties and no National Treasures in this record. A tiger was formerly in the Ryushido collection, and it and a toad carry box inscriptions by Ikeda Takao, a pupil of Kano Natsuo. Of a pair of of a monkey trainer the published sources write that it is a masterpiece in which one can fully savour the world of Nagatsune, and of a of Fukurokuju that the master shows himself at his true best. His signed and come to light from time to time, the far more rarely.