Open-surface droplet manipulation is essential for digital microfluidics, point-of-care diagnostics, and programmable microreactors; however, achieving robust, programmable, and multifunctional control remains challenging due to the absence of physical confinement and intrinsic directional bias. To address this, we introduce a magnetically actuatable Janus arrayed-microplate (M-JAM) platform that synergizes structural deformation with engineered wettability asymmetry to enable deterministic droplet operations by asymmetric capillary adhesion. The platform comprises an array of parallel microplates, each with a strongly hydrophobic side opposite a weakly hydrophobic side. This asymmetric design enables three core functions: rectified droplet transport, vertical capture/release via adhesion modulation, and on-demand splitting with tunable daughter-droplet volumes dictated by a scaling law. As a functional demonstration, M-JAM orchestrates a multi-step enzymatic glucose assay using only a reciprocating magnetic field, showcasing its capability as an integrated platform for microreactions and biochemical sensing. By coupling magnetic actuation with built-in surface heterogeneity, M-JAM provides a versatile, reconfigurable system for high-precision droplet-based automation and integrated bioanalytical applications.