Dungeons suddenly popped up across the planet, summoning invaders and monsters from alternate realities. Ancient gods slumbering beneath the Earth were woken. And all humans were empowered with Levels and Classes gained by, amongst other things, killing monsters and other humans.
Only a single instruction was provided by the System: “Whoever reaches Level 100 first shall become Earth’s new Overgod.”
So, a worldwide battle of epic proportions erupted... which Basil would rather sit out. Choosing the [Tamer] profession which allows him to speak with his cat, Plato, and other apocalyptic monsters, he'll adopt and train them to fight alongside him and defend his corner of the countryside.
After all, why bother fighting the apocalypse when you can tame it?