Legal Question in Intellectual Property in New York

Good questions, and you're thinking about the right potential problems. Unfortunately, though, there's no easy answer to the questions, and precious few bright lines.

If you're perceived by the trademark owners to be infringing on their mark, they'll probably come after you. But in deciding whether you are or are not, your best option is to have your work reviewed and compared to the existing work by a trademark lawyer - and to do so both before the coding/drafting stage and prior to releasing it.

Mr Browde is right on point. One of the concerns is that you state upfront that you're basing your game on this other game and you state there may be other similarities including the backstory of John's character which all sounds, at least in the area of gaming, like you could be infringing upon derivative or sequel rights which have been upheld by the courts (in the absence of a license) to reside with the original creator/owner. If it is a large company, they could have aggressive legal representation that may issue a cease and desist without regard to whether they'd actually prevail in court. You might consider going in a different direction with your app, or if you proceed as planned seek guidance from a lawyer with experience in copyright, trademark, and possibly some experience in gaming. Good luck!