Jirotaro Naokatsu signed his with a large six-character and dated them across the late- decades. The earliest of his designated works carries a Tenpo 2 date of 1831 and the latest an Ansei 2 date of 1855. He was a pupil of Naotane and later Naotane's adopted son, serving the Akimoto house of Tatebayashi in Joshu and living at Shitaya in . He first used the name Kazusa Taro and afterward changed it to Jirotaro, though the published sources note that no work signed Kazusa Taro has been seen. Through Naotane he stands in the Suishinshi line of Masahide, the central school of the revival. The published sources rank him within that line as the most capable hand after Naotane and Masayoshi, and a noted master in his own right. He died on the twenty-second day of the seventh month of Ansei 5, in 1858, the year after Naotane, at fifty-four.
The published sources divide his work broadly into and -, and his hallmark is the - modeled on the old masters. Its carrying feature is a taken from Kanemitsu. On one the published sources describe the temper as primarily , and judge that the aim was plainly Kanemitsu. Into that base he sets angular and pointed and ordinary , with long entering and intermingled. On four of his seven blades the temper slants in places toward . The that carries this manner is robust: a wide , little taper, a thick and an extended . On the long Tenpo 13 of eighty centimetres the published sources call the weighty blade in the hand truly martial. Of the Ansei 2 they write that in works of this type his is bolder than Naotane's and his larger, with a bright and at times clear .
Beneath the temper he forges a that packs well, at times an with areas of large and some . The lies thick and the steel is bright. An of some kind is named on four of his seven blades. Only on the long Tenpo 13 does a full stand. Elsewhere it is faint: a faint -like effect on the Tenpo 2 , a weak on the Tenpo 14 , and a pale -like effect over the -toned of the Ansei 2 . On the Tenpo 13 blade the published sources add that the pattern of the shows well and that the temper is set a little smaller and lower than usual, evoking an antique atmosphere. The enters and turns with a slightly pointed tip or a .
His work is not confined to the Kanemitsu model. The Tenpo 2 carries carvings unusual for him, a on the carved down into the tang and a on the . The published sources read it as aimed at the classical Nagamitsu, perhaps a copy of a lost original, and call it valuable as an example of his copies of masters other than Kanemitsu. They add that the angular and the partly slanting are 「彼の兼光写しに共通する手くせ」, a habit common to his Kanemitsu copies. A Tenpo 9 , made to order, shows the bolder side of the -. Its temper mixes many kinds of , the attaching well with coarse particles, and the and run longer than usual. The published sources call its large and slanting points to see in his work, as in Naotane's.
The other face is the -laden manner. A dated Kaei 5 and made at Suibara in Echigo has a mixed with and long . The attaches thickly, at places strongly enough to suggest , appears on the back, and the is bright and clear. The published sources call it 「直勝の本領発揮の一口」, the blade in which his true ability shows. A dated Tenpo 6, recorded in Honma's inventory of the Imperial collection, belongs to the same side: over an with a slight tendency, a temper mixed with deepens in the , with , , and . Its commentary adds that in Naokatsu's , as in Naotane's, there is often a swirling grain within the , and calls it a point of interest. On which of his manners surpasses his teacher, the published sources differ by date. The earlier designations say that his at times surpasses Naotane. The later ones say it of his - in the manner of the old Kagemitsu and Kanemitsu. Of the Ansei 2 they write that it stands beside Naotane's masterpieces of the type, calling it 「同作中の白眉」, the finest among his works.
For the collector he is a fine late- name held within a single rank. He has no National Treasures, no Important Cultural Properties and no . His designated record runs entirely through the , with six raised to that rank between the 18th session in 1969 and the 68th in 2022, every one of them signed and dated on an tang filed in with . A seventh signed and dated , of Tenpo 6, stands in Honma's inventory of the Imperial collection. Fujishiro rates him Jo-, and the Toko Taikan values his work at 450 points. The blades are in private hands, and none of his blades carries an old . Because his whole designated record is six signed , a Naokatsu of this quality comes to market only seldom. A - in the Kanemitsu manner, with its and , is the side of his work the published sources hold up most often.