Sairen (西蓮) is a swordsmith of Province, traditionally transmitted as the son of Ryosai and the father of Jitsua. In the Kozan there is recorded a bearing the inscription " no , Hakata Dangisho, Kuniyoshi Hoshi Sairen, Bunpo 1, second month," from which it is understood that Kuniyoshi and Sairen were the individual, and that "Sairen" represents Kuniyoshi's nyudo- (tonsured name). Among extant works, signatures include, besides the two-character "Kuniyoshi," such forms as "Dangisho Kuniyoshi," "Sairen," and "Dangisho Sairen." From these inscriptions he is considered to have been a swordsmith in the service of the Hakata Dangisho, which is thought to refer to the Chinzei Dangisho. One source further identifies him as the grandfather of , establishing a lineage of at least four generations of smiths working in the Kyushu classical tradition during the late period.
Sairen's manner of workmanship, like that of Ryosai and Jitsua, commonly shows a forging pattern of large scale in which the stands up and flows, with areas of and mixed into the . The tends toward a dark, blackish "kana-iron" tone, with fine adhering well and entering throughout; a faint whitish is frequently observed. The is characteristically a narrow -based temper in which the becomes frayed with , and the takes on an tendency — features that convey the traditions of Kyushu workmanship. Within the tempered edge, adheres well, and fine activities such as , , uchi-noke, and occasional or appear, producing a deeply engaging . The is typically with a turnback, often showing slight . Signed works survive in both and forms, though examples that remain with original signatures are extremely few.
Sairen's works are prized for their faithful preservation of the classical Kyushu style and for the depth of activity observable within the tempered edge, which — though rustic in character — yields a deeply flavorful and rewarding impression. Several blades carry appraisals of distinguished provenance: one bears the of Kotoku and was transmitted in the Tokugawa shogunal house; another, appraised by Kotsune at 150 in Jokyo 3 (1686), was transmitted in the Shigetomi Shimazu family; and yet another carries an by Kochu dated Hoei 2 (1705). That such prominent appraisers consistently endorsed attributions to this smith over the course of the period attests to the high regard in which Sairen's workmanship was held. Both and in the finest examples are in condition, and the internal activities within the tempered edge are exceptionally abundant, confirming Sairen's place as a smith of considerable importance within the forging tradition.