After successfully assassinating the King, Zhao Fu went to another Grassi Kingdom, which was one of the three Kingdoms neighboring the Lelai Kingdom.
These three Grassi Kingdoms had been waiting to see the Lelai Kingdom be destroyed in the past, and their relationship with the Lelai Kingdom was quite strained. After gaining control over the Lelai Kingdom, he had taken a step back and humbled the Lelai Kingdom's attitude, resulting in their relationship becoming better.
He was simply working together with those Kingdoms, so he did not feel bad at all for killing their Kings.
Zhao Fu went to the second Royal City and used the same method to kill that Kingdom's King. This shook the entire Kingdom, and everyone struggled for power. The commoners were all greatly unsettled, and the Kingdom descended into chaos. The Kingdom's Fate also descended into chaos; it was clear how important the King was to a Kingdom.