Accumulating lamination of weak attractive interactions is a crucial process for strategically altering the physical features of materials, which is an essential step in crafting cutting-edge functional electronic applications. In this study, we explore the electronic, Rashba spin splitting, optical, and photocatalytic properties of novel vdW heterostructure comprising blue phosphorene (P(blue)) and Janus monolayers (JTMDCs) like JMXY (Mo, W/X = S, Se; Y = Te) using first-principles calculations. We study two different stacking arrangements as Model-I and Model-II, which arise from the alternating order of chalcogen atoms at opposite surfaces in the Janus monolayer. AIMD simulations confirm the geometric stability of P(blue)-JMXY heterostructures at room temperature. All the investigated vdW heterostructures exhibit indirect bandgap and both models have Type-II band alignment calculated by weighted band alignment. Rashba spin splitting is observed in P(blue)-JMXY heterostructures, where Bader charge and work function analyses show that JMXY donates electrons to P(blue). Moreover imaginary part of the dielectric ε2(ω) function indicates that excitons predominantly govern energy conversions in visible and infrared regions. Furthermore, the promising photocatalytic activity of P(blue)-JMXY vdW heterostructures for water splitting under acidic conditions (pH=0) is demonstrated, with Model-I P(blue)-JMoSeTe and P(blue)-JWSeTe, as well as Model-II P(blue)-JMoSTe and P(blue)-JWSeTe vdW heterostructures being particularly noteworthy.