The human race has been advancing on dimensional portals to other worlds. So has the parallel universe

Then, it works. One brave soul goes through, and bring back another.

The 'alien' is named Seto, and boy does he have a warning for them.

'I'm powerful in my world. I go missing, you're gonna have hybrids and demons and Demi gods of all kinds on your heels. They won't listen to reason unless I'm sent back now.'

Sadly, they can't. The machine broke.

And they're coming for their sorcerer.

Seto will either help the humans, or let them fall beneath armies of soldiers.

They may call Seto a betrayer, or not

They may fight, or Seto might be able to stop both sides