Shunsui is Aizen’s Daddy… theory
Alright, imagine this: Shunsui might’ve been in on Aizen’s entire scheme from day one, thanks to Ukitake and his connection to Mimihagi. Since Mimihagi had the power to glimpse the future and was tied to the Soul King, there’s a chance Ukitake saw pieces of what was coming and shared these insights with Shunsui. Knowing Aizen was going to betray them, then lose, get sealed, and eventually be needed again could explain a lot about Shunsui’s attitude throughout all of it.
Think about how calm Shunsui always seemed. Even as Aizen turned against Soul Society, Shunsui never really seemed fazed, almost like he knew Aizen’s betrayal was just one part of a larger plan. It was more than his laid-back personality—he might’ve known that Aizen was essential to a future crisis. So when Shunsui went down to Muken to ask Aizen for help against Yhwach, it felt oddly smooth, like he was following steps he’d already thought through. Maybe he even convinced Central 46 that it was worth sealing Aizen instead of killing him, all with the idea of keeping him in reserve for something much bigger.
The kicker here is Shunsui’s comment to Ukitake about the kamikake being ready. It’s almost like they had some understanding that Ukitake would have to sacrifice himself and that Shunsui knew what that would mean for the Soul King’s stability. All his relaxed, almost detached behavior through the key battles, first with Aizen, then later with Yhwach, might’ve come from knowing the bigger picture—a resigned acceptance that he was just playing his role in a set of events that had to happen. So, Shunsui may have been acting all along with the knowledge that when things hit rock bottom, he’d release Aizen as a calculated move. For all Aizen’s ambition and danger, Shunsui probably trusted that Aizen would fight for his survival, even if that meant temporarily being on the side of Soul Society.
Shunsui might’ve gone to see Aizen even before all the events with Yhwach started to unfold, already knowing he’d have to recruit him when things went sideways. When he told Aizen they had a “common goal,” he wasn’t just talking about stopping Yhwach; he was hinting that, in a roundabout way, the Shinigami and Aizen were actually aligned in one specific goal—ending the rule of the Soul King. Aizen had always wanted to kill the Soul King to break free from the shackles of his existence, and Shunsui, aware of what was coming, knew the Shinigami were about to face that very dilemma, thanks to Yhwach’s plan to absorb the Soul King and take his place.
By the time Shunsui approached Aizen, he understood that Yhwach’s takeover was inevitable and that, ironically, Aizen might be the only person who could help prevent it—or at least, the only person who would have the resolve to challenge Yhwach, regardless of the cost. So, in a way, Shunsui played Aizen’s ambitions to his advantage, banking on the idea that Aizen’s hatred for the Soul King would make him the perfect, if dangerous, ally. It’s almost like Shunsui had everything mapped out from the start: the betrayal, the sealing, and the eventual release—knowing full well that Aizen would step in when it mattered most.
