This study proposes a concept for on-demand manufacturing of soft mechanisms using laser technology for welding and cutting plastic sheets. Soft mechanisms, which are known for their flexibility, compliance, and lightweight properties, have been explored in various fields. Despite advancements in soft robotics, challenges such as lengthy production times, complex fabrication processes, and reliance on specialized expertise persist. Laser processing is a prominent technique for the fabrication of soft mechanisms, particularly film-based mechanisms, in terms of production time and manufacturability. Such methodologies are considered innovative; however, they remain underexplored. This study advances laser methodology by introducing a novel on-demand production approach that leverages laser-based techniques to fabricate multilayered soft mechanisms from plastic sheet materials. The feasibility of this concept, applicable to both small and large mechanisms, was validated using a commercial laser-cutting machine. We successfully fabricated a range of soft mechanisms, including a peristaltic robot capable of moving at 3.3 mm/s while carrying a load of 1.2 kg, and a stackable valve mechanism that switches flow paths using a plastic leaf spring and an inflatable airbag, both constructed from multiple plastic sheets. Key contributions of this study include the development of innovative fabrication protocols for soft mechanisms and multiple examples demonstrating the versatility of the technique. This study advances the field of soft robotics by providing a practical and efficient solution for manufacturing complex, large-scale soft robots with potential applications in space exploration, industrial automation, and other unstructured environments.