  Let $M$ be a hyperK\"{a}hler manifold equipped with a $U(1)$ hyperK\"{a}hler
isometry, and let $I$ be a complex structure on $M$. In this note, we study the
$A_{\infty}$-category of A-branes for the Landau-Ginzburg model with target
space $(M,I)$, and superpotential being the $I$-holomorphic moment map. We show
that if $I$ is a generic complex structure, the $A_{\infty}$-category is
semi-simple. For exceptional complex structures, though typically not
semi-simple, the category still has no instanton corrections. We illustrate the
$A_{\infty}$-category at both generic and exceptional loci when $M$ is the
cotangent bundle of the projective line.
