Born to Soga no Emishi and heir to three generations of Soga power built since his grandfather Umako, Iruka grew up at the center of court politics. He deepened his father's grip on government, intervening in imperial succession disputes. In 643, he surrounded the residence of Prince Yamashiro no Oe—the most credible imperial heir and son of Prince Shotoku—and forced the entire clan to suicide. This act of near-regicide inflamed resentment throughout the court. He compounded the outrage by styling his mansions with quasi-imperial titles and allowing his father to wear a purple cap, mimicking imperial ceremony. These usurpations accelerated the conspiracy of Prince Naka no Oe and Nakatomi no Kamatari. On the 12th day of the sixth month of 645, during a ceremony receiving envoys from the Korean kingdoms at Asuka Itabuki Palace, Iruka was cut down before the eyes of Empress Kogyoku—the Isshi Incident. The following day his father Emishi burned his mansion and died. The Soga main line was extinguished, triggering the Taika Reform.

Driven by lust for power, he overstepped even the imperial family. He reportedly named his mansions with imperial-style titles, mimicking the throne.

Symbol of the Soga clan's downfall. The Isshi Incident is Japan's greatest ancient political upheaval and became the starting point for the ritsuryō state. Remembered as a cautionary tale.