五代目川井長左衞門正冬のとき大坂夏の陣の功により元和七年（1621年）５月郡山城主松平下総守忠明（徳川家康の外孫）より今井の西口にあることから今西姓を名乗るようにすすめられ、その時に薙刀銘来国俊を拝領している。

In late June or July 1621 during the time of the fifth family head Nagazaemon Masafuyu, in recognition of his achievement in Osaka Natsu no Jin (Summer Siege of Osaka), Masafuyu was given recommendation by the lord of Koriyama-jo Castle Shimousanokami Tadaaki MATSUDAIRA (a grandson of Ieyasu TOKUGAWA) to assume the new surname of Imanishi deriving from his house being located at the west (nishi in Japanese) entrance of the town of Imai and, in addition, received a gift of naginata (Japanese halberd) made by the grand master swordsmith Kunitoshi on that occasion. - Wikipedia日英京都関連文書対訳コーパス