The Beastmaster Hero; Zookeeper

The world used to be normal, but then the Last Christmas happened.

A lightning storm covered the entire planet, those lightnings being actually rifts to other dimensions created by the power of creatures known as Patrons.

The world soon became akin to an RPG as the planet expanded to boundless levels and multiple new humanoid species appeared, every sentient being in the planet being taken into the Class System.

But the real impressive ones are the people and animals who got hit by said lightning storm, as well as their descendants.

Struck, people who got affected, gained superhuman powers from one or more of the ten Patrons, while animals mutated into Monsters.

Dungeons similar to pocket dimensions filled of those monsters started to pop up, and society changed forever with the rise of the first heroes and villains.

It seems that while people suffer no side effect from just the Class System, becoming Struck gives them a drive for conflict, which led to heroes and villains becoming common careers for Struck.

A few decades have passed since and while some older folks remember the days none of this existed, the world is nothing like that anymore.