Here is an overview of the game’s story, via the official website:
You are a beta tester for the virtual reality game “Soul Divers.” As you progress through the game, you start to notice that the game’s world is real. After meeting a mysterious woman named Rania, you learn your mission. To carry out your mission, you must confront powerful enemies and rebuild the kingdom… Is it possible to save the connected two worlds from ruin?
Read more about Ni no Kuni: Cross Worlds here.
Watch a trailer below.