So this happened when Reina and Cade were left alone without Amber.
There are actually two first times here, one for the sexy times between the two without the main instigator, the other is for Reina's satisfied curiosity.
What usually happened during the undetermined number of intercourses before this situation was that those two ended up in the same convenient place at the same convenient time and near the same conveniently horny half-lynx. This time they took matters into their own hands. I'm sure it wasn't their intention at the beginning... or maybe it was? who knows. :D Once thing lead to the other and Reina ended up satisfying one of her curiosities.
There's a longer and more detailed story about that in my head, but I suspect you care very little about that, just enjoy the picture :D