Hey, just using this as an place to flesh out the basic, not too spoilery things about Yuno and the world he occupies

Yuno's world is one that has been through two cataclysmic events. The first cataclysm introduced magic- essentially a psychic, reality altering force, into the world. This was a world that previously was very much like our "real" world, but magic completely threw off the balance and things got weird. The natural laws of science started to warp, people and animals began to change in impossible ways, wars broke out, it was essentially the apocalypse and the end of society.

While some beings made it through, none had as much success as the wizards- those with the ability to hone magic. It was a group of wizards who, in a sympathetic attempt to reverse the flow of this new chaotic and magical timeline, unintentionally brought about the second cataclysm- the end of that reality as anyone knew it, shattered into ideas, memories, echoes of existence.

But something managed to hold these remnants of reality and conscious life together, like a bubble around a cloud of vaporized existence. And somehow, a new world took shape, sewn loosely together with the very psychic life-force that destroyed it- magic.

This is where Yuno finds himself at the beginning of his story, a confused being stuck to the body of a plush cat, and with overflowing magic that alters his reality into an unbearable nightmare that he must figure out how to control. If he can, his abilities could help sew reality back together- but if he fails, the whole world could unravel yet again.