My Sister Was Killed, and I Let Monsters Sweep the World!

Three years ago, the virus broke out and the beast mutated. In order to protect the world, Xia Yi and her sister followed the team and entered the restricted area to fight mutant monsters. After making huge sacrifices, they finally eliminated all the monsters in the restricted area and completed their mission gloriously. Just as Xia Yi led the remaining troops to return in triumph, what was waiting for them were tanks one after another, aiming their guns at themselves! They were supposed to be heroes, but they were betrayed! In the bombardment, Xia Yi lost his sister who had been dependent on him for many years! The remaining teams were all wiped out! In the end, only Xia Yi survived! "Ah!!!" Xia Yi looked up to the sky and screamed! Why did God do this to him? He had no choice but to carry his sister's body back to the restricted area. At this moment, Xia Yi discovered the source of the virus. As long as you upgrade, you can strengthen the monster. So, he decided to let monsters sweep the world! He wants those people to regret the choices they made!