might be a wrong guess but the game did tell us in the start that reapers can go into the light after they have collected energy (by reaping ghosts) and completed their ghosts.
which (spoiler) the end boss has supposedly done.
so, maybe before fighting the end boss, if you acually get all the upgrades and skills and stuff and therefor "complete your soul", maybe the final scene might be different?
That's about the only thing I can imagine happening, otherwise I cant imagine how to find any other ending :-/