  We study de Rham prismatic crystals on $(\mathcal{O}_K)_{\bbold{\Delta}}$. We
show that a de Rham crystal is controlled by a sequence of matrices
$\{A_{m,1}\}_{m \geq 0}$ with $A_{0,1}$ "nilpotent". Using this, we prove that
the natural functor from de Rham crystals over
$(\mathcal{O}_K)_{\bbold{\Delta}}$ to the category of nearly de Rham
representations is fully faithful. The key ingredient is a Sen style
decompletion theorem for de Rham representations of $G_K$.
