Reynard and Leon sometime after they teamed up to find Emmerson. They're chasing someone(something?) case relevant and they are NOT catching up.
In fact, Ren is progressively looking worse as they try to keep up, and Leon is torn between frustration at the person/thing getting away, and concern that his new friend looks like he's going to pass out.
Leon catches Ren when he finally collapses, but instead of passing out, he lurches and throws up some 4-5x his bodyweight in black water. All Leon can do is hold onto him and watch in mixed horror and awe as limbs and figures form from the dark liquid and give chase to the thing they were after...
Fun way to find out your new guy is full of weird ghosts who also want to help you find your partner.
(Edit) Additional thoughts:
Reynard's ghosts aren't really self aware.
They're a mix of memories and instinctual impulses that eventually bind so tightly to Reynard that they become an extension of him.
Reynard has very little control over it all at first. They'll extend on one side of the plane, allowing him to see around corners or into other places in the mortal/material side of the plane. Which is cool, but it's like being smashed in the face with a brick made of deja vu out of nowhere.