God's Favorite Game Heaven Series

World's Dungeon had infested Earth with powerful creatures in the 20th century. Humans called this disaster part of [God's Favorite Game].
Humans worked hard to kill all the creatures. When the first creature fell, that's when they realized their potential for growth.
The killed all the creatures residing on Earth until there was none left. The only things remaining was the World's Temples from where the creatures came from.
*
It is now the 21st Century and Yuan Tai was going to use the World's Dungeon for his own benefit.
[Occupation Unlocked!]
[You have become 'The Thief'!]
"Damn, a thief occupation? I won't become strong at all! What's so good about being able to steal!" complained Yuan Tai.
[...]
.
Cover is not mine, kudos to the person who created it.