Start the game with Overlord fusion, and become stronger by killing enemies

Xu Qianqiu traveled to a world where humans and demons coexisted.
He started out as the eldest prince of a kingdom. Who would have thought that this kingdom was facing an invasion by demons, and more than 40 cities were broken in a row, and it was in danger, and the king actually asked him to lead troops to attack the demons.
Fortunately, the strongest enemy killing system was activated, integrating the power of the overlord.
From then on, this world had one more crazy killing god!
"Congratulations to the host for killing the demons and obtaining the Eighteen Riders of Yanyun."
"Congratulations to the host for killing the demons and obtaining the Tiger Roaring Dragon Roaring Iron Cloth Shirt."
"Congratulations to the host for killing the demons and obtaining the character card Li Cunxiao."
…………
Xu Qianqiu led his army to defeat the demons and regain the lost territory, but just when he was about to hit the demons' lair, the court actually signed a peace agreement with the demons and ordered him to call off the troops.
Xu Qianqiu looked towards the direction of the capital with a dim gaze. You know, he can not only get system rewards by killing demons... but also by killing people! !