[ Synopsis ]
The deity and the group organized for the task fails to defeat the demon lord.
Years passed, the humanoids slowly lost their territory, as the average of demonic strength kept rising, humanoid races were only succeeding in resisting the demon kind so much thanks to the only hero who remained. Summarily, it was a bad time that was getting worse.
Eventually, the deity that was formerly at the top returns to the world.
Main concern. Get power to defeat the demon lord, and bring some level of peace.
Accidentally, the deity ends up connecting the space between the world and another world.
It was a bit of a problem, but some people were brought from that world, though since so much power was used to bring them over, the deity couldn't just return them.