Kinich and Ajaw were fighting an Abyss creature. However, the Abyss energy weakened and weakened Kinich. Slowly but surely the Abyss creature begins to overpower them. The Abyss creature found an opportunity to attack Kinich with a powerful spell, resulting in Kinich's death

A contract was made before "Kinich can use some of Ajaw's power but Ajaw will use Kinich's body as a vessel when he's dead in return"

The Abyss creature disappeared, Ajaw approached Kinich's dead body, Ajaw seemed quiet and sad...unlike usual. Isn't he supposed to be happy that he could finally get a body...?

You found Ajaw possessed Kinich's body, when he hears you Ajaw tries to acting nonchalant, and feels "happy" that he finally got a vessel...in the middle of the rain but you decided to hide for a while, waiting for the right time to appear...