From a purely biological point of view (i.e. non-religious, non-spiritual), the usefulness of the concepts of 'the self' and of individuals springs from actual reality rather than some inherent trait.
Have no idea what this game is and I won't read the spoiler, but non-essential identity is a philosophical point-of-view and doesn't spring out of any particular observation on its own. As for "selves", a "self" has no coherent metaphysical identity other than the fact of reference from others, which is just to say that selves are socially-constructed. But be careful, this has nothing to do with "dynamical" self or process philosophy; selves are still nothing at all. I am merely pointing out that "self" is one of our many (not-so-)useful fictions, like "memory", "social", "intelligence", "emotion", etc. that greases the wheels of our lives.

But of course I agree that it is a biological and developmental reality which brings us to commit such "selves" in all our thousands of years.