2500 years after seven worlds merging

This is a story where seven different worlds have merged due to one big event. Each world has different circumstances, storylines, settings, and systems. There was one world where it was the magic world, there was also the esper world, the sword world, the robot world, the eternal winter world, the apocalyptic world, and the supernatural world. And the unification of the seven worlds creates an even greater chaos, in which people from each world who had originally been threatened by their enemies, now they have to face another enemy again. It makes humanity from every world unite to rebuild a powerful civilization.

Arde, is an adventurer and he is the protagonist of this story. He initially ventured alone, and lived a boring life as a solitary adventurer. He is always haunted by his dark past. But everything changes after he meets a mysterious girl who claims to be from another branch of Destiny, or a parallel world. The girl tells Arde a shocking secret, and it motivates Arde to stay alive and become stronger. From that moment on, Arde's life begins to change, and he begins to gain a new purpose, which is to save the person he cares about most, whom he considers to be dead. There are many dangers that await him, in this huge and diverse world.