The Kingdom Hearts universe is a strangely dense and complicated one, despite its outward appearance of being very child friendly, what with the Disney characters and bright colours. But beneath that façade of happy-go-lucky fun, lies a surprisingly deep and interconnected series of characters and narrative threads that keeps the fan base speculating and theorising.
The general plot of Kingdom Hearts III has been loosely alluded to as narrative structure that will pave the way for the “Key to Return Hearts”. This may well be another one of the infamous Keyblades and this may also be somehow related to Sora’s Heart. I don’t claim to be an expert on the matter, but from what I gather Sora’s heart which is effectively a prison. Inside this prison is Ventus (sometimes called Roxas). The catch of this heart prison is that it’s fairly easy to enter, but not so easy to leave. So with that it mind, YouTube user HMK made this video based on a personal theory.
The theory posits that there is a way for Sora to release Ventus from his own heart. He will then make use of this ability to release other individuals from other hearts. Speculation of course. Heaps of salt and all that good stuff. Kingdom Hearts 3 does not have a release date yet but is expected to arrive on the PS4 and Xbox One.