"What can you gain from cooperating with me?"
Aizen, of course, noticed that Su Xiao showed sincerity in cooperation. In this fish-or-death situation, he wouldn't immediately tear faces with Su Xiao, and he was very interested in those '500 purity' Spirit Particle Balls Su Xiao mentioned.
"Gain what..."
Su Xiao paused for a moment, shaking his head.
"I can't think of what I might gain for now, but at least I won't add an enemy I must eliminate. Your goal is to overthrow the current rulers of Jingling Court, while mine is the Zanpakutō. It seems there's no conflict, quite the opposite. If I assist you, there's a greater chance to acquire a Zanpakutō. Of course, if you want my help, produce an equivalent amount of Zanpakutō."
"Indeed, our goals don't conflict; we need not oppose each other."
As things developed to this point, the killing intent in Aizen's eyes vanished. On the contrary, he found Su Xiao to be a good collaborator.
