  To a smooth, compact, oriented, properly-embedded surface in the $4$-ball, we
define an invariant of its boundary-preserving isotopy class from the Khovanov
homology of its boundary link. Previous work showed that when the boundary link
is empty, this invariant is determined by the genus of the surface. We show
that this relative invariant: can obstruct sliceness of knots; detects a pair
of slices for $9_{46}$; is not hindered by detecting connected sums with
knotted $2$-spheres.
