Nagayoshi is the swordsmith of the Momokawa (桃川) group of Echigo province, working in the period, and he survives in only a small number of signed blades. Momokawa is a place-name in Echigo, and the published sources record that smiths styling themselves Nagayoshi (長吉) continued there for two, perhaps three generations from the into the period. Their output was scarce, and among the extant works there are no dated examples, so the several generations who bore the name cannot be told apart. One tradition makes him a pupil of Kanro Toshinaga (甘呂俊長) of Echigo, but the published sources set that tradition gently aside on the workmanship, finding little in his work that resembles Toshinaga and reading the and as Yamato (大和風) in character instead. He is therefore read not by his teacher line but by his own hand, which is consistent across the three forms in which he survives, a , a and a .
That hand is, before anything else, a Yamato hand carried into Echigo steel. Over the body the published sources describe a (直刃) base, narrow on some blades and wide on others, the frequently frayed with (ほつれ), and along it (砂流し) and (金筋) run while the stays bright. It is a quiet, restrained temper, far from the showy of contemporary , and the persistent and the streaming are exactly what mark the work as Yamato rather than . The follows the idiom, swept with and turning sharp at the point on the and , or finishing in a small (小丸) with on the , tempered down long on both faces. The carries the antiquity as the temper, an (板目) mixed with (杢) that runs and flows into a grain (流れ肌), standing slightly toward (肌立), and on the the flow opens into an (綾杉) appearance, the steel tending whitish (白け). This standing, flowing, whitish is the constant of the work, the feature that ties the three forms together and the one that separates the Momokawa hand from the smiths of the period.
The surviving blades divide into two registers of the one manner. The rarer is the signed , a blade with and a , almost , that cuts the long signature toward the and carries narrow grooves (細樋) along the with a plain (素剣) in raised relief; over its tight the mixes small (小互の目), with (地景) and a bright (匂口明るい). The more numerous register is the and , broad and of slightly extended proportions (寸延び), the with a finely chiseled two-character (二字銘) below the and the with the place-name in a five-character signature (五字銘); on the a grass-style (倶利迦羅) is carved on the and a (梵字) with (護摩箸) on the . Of the the published sources judge that it well demonstrates his characteristic style, writing that the blade 「長吉の作風をよく示しており」, the with frequent and taken as the very signature of his manner. The generational question is left open, the literature recording dated examples of the Joji era (貞治) while the extant and are exceedingly few and undated.
For the collector, Nagayoshi is a thin and quiet name rather than a celebrated one, and the honest measure of him is the small body of work on record. The reference texts place him in the Toko Taikan but record no Fujishiro grade, and there is no National Treasure, no Important Cultural Property and no among the designated work; the official record runs to three blades, the , the and the by which his hand is read, with no provenance to houses recorded among them. The signed pieces that survive were held privately, in Niigata and in Shizuoka, when they passed , and a Momokawa Nagayoshi is met only rarely and almost always signed. Of the the published sources note that it is 「同名中でも時代が古く」, an early and rare survival of the name, while of the rare signed they write 「現存数少ない長吉在銘の太刀として」 its value as reference material is extremely high. When one comes before a student of the northern provinces it is a quiet find rather than a landmark, valued for what the published sources call it, 「長吉研究の好資料の一口である」, an honest and uncommon way to hold the Yamato manner as it was practised far from Yamato, on the Echigo coast.