Okay, so here's a question that's been on my mind for a long time now; what exactly makes the Humans and Hollows polar opposites, and what makes the Shinigami and Quincies polar opposites? By the looks of things, it's on a molecular or cellular level, and not something trivial; this became evident by how Urahara stopped the souls of the Vizards and Masaki from undergoing "Soul Suicide"...

The most intriguing thing, in my opinion, is finding out the origin of either the Shinigami or the Quinices; due to the fact that they're polar opposites of each other, it would make sense that either the birth of one race caused the birth of the other, or they were born at exactly the same time...

There's something connecting Yhwach and the Soul King; that's one thing I'm 100% certain about! It's just odd that both characters seem to have been "hibernating" up until recently; that says to me that they're "equivalent opposites" (such as the same pieces on a chess board but opposite colours), or they're both parts of the same thing (for example, they're perhaps parts of a single consciousness, which means they sleep and awaken at roughly the same time).