Matsumoto on Gin, briefly, at the end of the world; spoilers for chapter 178.
He congratulates you when you're promoted to vice-captain of the tenth even though by the creasing of his long narrow eyes you can tell he sees no glory in serving as Hitsugaya's sidekick. "You should have been /mine/," he says once, and you feel the butterfly pressure of his thin bloodless fingers on your arm as though to punish you with the fact that although he looks and feels like a man made out of a single sheet of rice paper it is he who lays the claims, he who has the power to back them up, he who choses not to. Of course you have to laugh with the rest of them even though their faces are stiffer and more uncomfortable than yours. He looks at you and lays his finger beside his cheek and behind the lank fall of white hair over his face you suddenly realize you can see one bright eye open and looking at you, only you. You have both grown too old to keep this kind of secret cleanly in your hearts but you humour him because you were young together and that is the heaviest currency anyone can trade with you. This was before his smile changed into something that looks like it's been cut into his face with a knife; you can't even guess whose hand guided the blade until it is too late. For the longest time you were afraid that he had guided it himself. But even this fear cannot change how every time you see his face you think of those nights when the crickets will not let you sleep for the sound of their love and you leave your door unlocked but no one ever comes through them and you see yourself living forever in this endless circle of cold mornings and identical afternoons and terrible lonely nights kneeling for eternity in the guillotine of hope. You are never sure what it is that you are hoping for because you already know for certain that he loves cutting people open, cutting them sideways and up and down, cutting their beating hearts carefully out of their chests and showing them the whittled bones of their own legs, making patterns in dust with the blood on the tip of his sword, destruction, disorder, chaos, and you.
At the end of the world, when you see him joining Aizen's ascent to madness, you understand what it is his face and curving knife-carved smile and pale butterfly fingers have been saying. It's our secret, his one open eye winks; you should have been mine, but even then I was already his.