Ghost center and representations of the diagonal reduction algebra of $\mathfrak{o}\mathfrak{s}\mathfrak{p}(1\mathrm{\mid }2)$

Reduction algebras are known by many names in the literature, including step algebras, Mickelsson algebras, Zhelobenko algebras, and transvector algebras, to name a few. These algebras, realized by raising and lowering operators, allow for the calculation of Clebsch-Gordan coefficients, branching rules, and intertwining operators; and have connections to extremal equations and dynamical R-matrices in integrable face models. In this paper we continue the study of the diagonal reduction superalgebra $A$ of the orthosymplectic Lie superalgebra $\mathfrak{o}\mathfrak{s}\mathfrak{p}(1\mathrm{\mid }2)$. We construct a Harish-Chandra homomorphism, Verma modules, and study the Shapovalov form on each Verma module. Using these results, we prove that the ghost center (center plus anti-center) of $A$ is generated by two central elements and one anti-central element (analogous to the Scasimir due to Le'{s}niewski for $\mathfrak{o}\mathfrak{s}\mathfrak{p}(1\mathrm{\mid }2)$). As another application, we classify all finite-dimensional irreducible representations of $A$. Lastly, we calculate an infinite-dimensional tensor product decomposition explicitly.