This research explores the synthesis of Mixed Reality (MR) and Human–Computer Interaction (HCI) technologies to create an advanced assistive device aimed at enhancing grip stability for individuals with Rheumatoid Arthritis (RA) and Osteoarthritis (OA). The device incorporates MR with a servo motor locking mechanism, offering enhanced grip assistance crucial for maintaining autonomy and improving quality of life. By integrating digital overlays providing real-time instruction and feedback, the device not only supports physical handling but also enriches the rehabilitation experience, making it more engaging and personalized. This paper details an iterative design process that merges ergonomic design principles with sophisticated engineering, illustrating MR’s critical role in improving digital and physical interactions. Preliminary feedback from users has shown notable improvements in task performance and satisfaction, highlighting the device’s ability to increase independence and alleviate user discomfort. Overall, this study underscores MR’s significant potential to revolutionize assistive devices’ functionality, leading to greater independence and an enhanced quality of life for individuals with RA and OA.