The Seven Tigers were a group of Shogunate-era generals who nearly stopped the Scarlet Empire before it began. After the Great Contagion and the reactivation of the Imperial Manse by the Scarlet Empress, the entirety of Creation held its breath. The Shogunate was inarguably over - taken down by a combination of plague, the Fair Folk and the reintroduction of weaponry an order of magnitude more powerful than anything used by the rapidly decaying Shogunate forces.
At this time, it wasn't entirely certain what was going to happen next. The Empress might have the weaponry, but at least initially she didn't have the manpower and in the early days of her nominal reign, seven former generals of the Shogunate launched an invasion of the blessed isle. The Seven Tigers revolt was the first real test of Imperial power.