Soft actuator is the main technology that drives the development of soft robotics as it defines the capabilities of soft machines. One of the key challenges in soft actuator research is to simultaneously produce complex morphing (e.g., surface morphing) and high force. Therefore, a soft robotic pad (SRP) was developed as a new soft actuator that can potentially tackle this challenge. This article demonstrates the highly flexible customization process of the SRP regarding fabrication, morphing design, and force scaling for a challenging application: a giant manta ray robot with the Mobuliform swimming mode. Soft robotic pectoral fins (SRPFs) are customized using the SRP technology for the robot. Detailed characterization results show that the SRPFs can generate almost 100 N force or 25 Nm torque with a dual curving motion to mimic the manta ray fin kinematics. The SRPFs are able to propel the manta ray robot to a decent swimming speed with biomimetic fin motions. As a new member of the soft actuator family, SRPs exhibit strong capabilities through this manta ray robot, and they can potentially become unique tools for many engineers and researchers to tackle challenging applications requiring high force and surface morphing.