I noticed some similarities with the soul king and hogyokou Aizen... They both have something to do with caterpillars and butterflies.
No, seriously, they called the palace the soul king is living in a cacoon like structure, the soul kings eyes are kinda like Cacoon Aizens, and the person talking to the soul king asked if he was awake yet, like awaking from a cacoon and hatching. Plus, Aizen's later forms had to do with butterfly like appearances, and his cacoon form was human like, just like the soul kings.