Quick Transmigration Observer

The world Lu Sanshan originally lived in was turned into an apocalypse by two transmigrators. He awakened an ability in the apocalypse and eventually defeated the two transmigrators and their System. Because the mission had failed so badly, the System couldn't leave that world, so it was forced to bind itself to Lu Sanshan, a native of that world. It took him through the Myriad Worlds, but since it couldn't take on any missions, all they could do was watch one transmigrator after another call the shots and slaughter their way through their mission worlds.

The only upside was that Lu Sanshan didn't have to be forced to complete missions, leaving him plenty of time to enjoy life.