Sounds like a good premise. I can imagine really enjoying your shit in a few demodays once some of the story is in. As for the main character, being someone who ideologically should be on the creatures side, the ones who do not want a wish but just want to maintain purgatory, what are his motivations?
Thanks, if you're asking why is the main character trying to end the world, he's doing so not for the wish but just to prove a point, he's angry at people for treating him as less than nothing all his life, him "winning" against the people protecting Purgatory would making him prove to himself and everyone that he can be better than them regardless of what they think of him. If you're asking why people are trying to maintain the purgatory, it can be for many reasons, one of the bosses you'll have to execute (SPOILER WARNING:) will be a girl who's power is to give life to dolls and plushies, making them her family. She pleads for you to stop your crusade against the world and spare her and her friends, of course, the main character won't flinch and the boss fight will ensue. I hope that answers your question.