I'm sure whatever wish the brother gets granted by that deity/demon following him around will be a "careful what you wish for" type wish. Where the wish is taken a little too literally or taken in a different context. The deity/demon will probably say "this is what you wished for, I kept my word" even though it's totally not what the boy wanted. All in all things are starting to look like they're heading toward a train wreck.
I'll stand by my earlier guess that the Master will either die or be crippled and that the sister will probably be the key to the situation but at the same time expose herself to the demons prompting her abduction or loss of power. But now on top of that I see a mix of disaster perhaps tying it all together by whatever the brother requests of the deity/demon.