Being is normally thought of as the underlying substance of an objective phenomenon, that which anchors it in objectivity. If you don't like the idea of 'substance' or hypokeimenon then it is the actuality that distinguishes this phenomenon from all else in the realm of possibility, it is not merely the choice, but the bringing forward or accomplishment of the choice. All of such notions belong to models of reality, that is to mental constructs designed to explain the mystery of what stands against awareness. The phenomenon at the core is the standing over against awareness but also in awareness. Put simply it is the phenomenon looking back at you as you look at it. The only thing that needs to be revealed is what awareness, this very awareness is, or rather, how it acts.