Warring States Spycraft: My Intelligence Network Gives Me Power over the Seven Kingdoms

I transmigrate to the Warring States era, where I am the most dangerous shadow among the Seven Kingdoms. The King of Qin sees me as his sword, my closest friend sees me as his shield, and my beloved sees me as a mystery. All I want is to leave an undying flame for the world a thousand years from now, amid this raging torrent.