I've been wondering for some time now about how the wall between shinigami and hallow stems. To that end i have come to wonder that with hallows existing as a mass of souls energy and memories that when a soul is purified by a zanpakuto where does this mass go. My belief is that this mass is sealed by the will of the zanpakuto and as the soul rediscovers the mass that is sealed away , that this is the key to becoming a shinigami and that zanpakuto spirits may in fact be the collective mass said person had once consumed given it's own conciousness by the master's will so to speak. So in short only those who had once been hallows previously can become shinigami. Since we have a greater understanding in how hallows evolve through a canniblistic festival involving consuming hallows of the same type till one dominate mind becomes head to the mass. I can then conclude these higher levels constitute who has the potintial to achieve bankai as the soul struggles to conquer it's past sins and become master of it's own fate hence our chain of fate. I would love to hear your ideas and critisism is always welcome and thank you for your time.