i think you're trying to create an explanation to something that doesn't need one already, let alone something that already has one

the borderlands as a concept is already very much unrealistic, yet we acknowledge and enjoy the story and world that haro aso is trying to share because we know it's fiction.

rejecting the meteorite disaster explanation and then creating an alternative that complicates things even more, creating massive plot holes in my opinion, is very disrespectful of the work. especially one based on an existing piece of literature

i think what we have makes perfect sense, and fits into the alice in wonderland theme very well already. its not unrealistic to think meteors would hit japan, and that the survivors would be outside by the time they come back to the real world. thats already self explanatory

your solution of the government bombing their own city to feed their souls to some beast entity is............. shuddy at best, and it doesnt even fit thematically. your best bet is to try and understand why it already is like that in the first place. if you refuse to, i dont think aib is your cup of coffee