The latest issue of VJump recaps a bit of the info we already know about Zabida, the Kamui fusion system and the relations between characters.
Slay and the others apparently meet Zabida as an enemy or an opponent. Whether this is true for the entirety of the game, we don't know yet. Zabida is apparently a dangerous Divine who's willing to fight against the Priest without holding back. Being a Divine of the Wind element, it is mentioned that he also has a similar fighting style to Dezel.
An updated relationship chart between the characters is out. The main contract is between Slay and Lyla. Lyla has a contract with Mikulio, Dezel and Edna, with Lyla as the Shushin and the three as her Baishin (more info on that here). Alicia forms a contract with Slay, becoming his Juushi where she is given some of his powers. This allows her to see the Divine, finally. Slay is, obviously, the Priest, and there's a ???? relation between him and Zabida.
Here's a closer look at Slay's Kamui form when he fuses with Lyla. It's not mentioned, but the art seems to be by Okumura?
Tales of Zestiria will be released in Japan, North America and Europe sometime in the future. Pre-orders are now available at the following shops: