The head of the Iriki-in clan and the son of Iriki-In Shigetoshi, Shigetomo was a vassal of the Shimazu family of Satsuma. In 1526 the Shimazu lord, Katsuhisa, suffered the rebellion of a kinsman, Sanehisa, and was forced to flee Satsuma. Katsuhisa was succeeded by Takahisa, but continued to wield some authority from the sidelines. Shigetomo, whose lands were close to those of the splinter Shimazu, fought a series of battles with Sanehisa around Momotosugi. In 1536, no doubt to encourage the Iriki-In onward, Katsuhisa 'awarded' Shigetomo Momotosugi castle, which at present was actually in the hands of Sanehisa. The following year, Katsuhisa further awarded Iriki-In with Koriyama castle, although this location would not require an assault to enter.
On 9 October 1539 Shigetomo stormed Momotsugi in a night raid and earned himself both the castle and the respect of Shimazu Takahisa. By the end of the year Shigetomo had taken a number of Sanehisa's forts (including Hirasa, Kuma no sho, Miyasato, Tazaki, and Takea) and taken the Iriki-In clan to a place of prominence within Satsuma. Over the next few years, however, relations between Shigetomo and Shimazu Takahisa soured, and rumors flew that Shigetomo was plotting a rebellion, even though Shigetomo's younger sister was the wife of Takahisa and mother of the Shimazu heir, Yoshihisa. In 1544 Shigetomo died, and shortly afterwards Takahisa took Koriyama Castle, ending the brief Iriki-In 'golden age'. Shigetomo's successor, Shigetsugu, managed to restore favor with the Shimazu and the Iriki-In would fight under the Shimazu banners in Yoshihisa's efforts to conquer Kyushu, abroad in Korea, and at Sekigahara.
- Initial text from Samurai-Archives.com FWSeal & CEWest, 2005