J.J. Sexton served as a scientist for the Principality of Zeon during the One Year War. He led the "Reuse P. Device" (RPD) initiative aboard the Zeon Papua-class flagship *Dried Fish*, assigned to the prosthetic-limb reliant Living Dead Division. The RPD was a next-generation operating system enabling direct neural interface for mobile suit control, even by inexperienced pilots. Sexton viewed the division's amputee veterans as ideal, expendable test subjects for his research, treating them as lab rats. His approach revealed a driven, selfish, and ethically compromised nature. As combat against the Earth Federation's Moore Brotherhood in the Thunderbolt Sector intensified, Sexton prioritized the RPD project's completion above all else. After Living Dead Division ace Daryl Lorenz lost an arm, Sexton lobbied division commander Captain Burroughs and scientist Karla Mitchum to pressure Lorenz into voluntarily amputating his remaining natural limb. This drastic measure aimed to boost Lorenz's synchronization with the experimental RPD-equipped MS-06R Zaku II High Mobility Type, highlighting Sexton's willingness to sacrifice others for technological gain. Facing the *Dried Fish*'s destruction, Sexton revealed profound cowardice. During evacuation, he callously pushed aside a wounded soldier to secure an escape pod for himself. While many pods were destroyed by Federation forces, Sexton survived, recovered by a vessel from the post-war South Seas Alliance, a faction emerging from the Nanyang cult. He defected to this group, leveraging his expertise to become one of their chief scientists. Within the Alliance, he resumed RPD development, creating new variants of the Reuse "P" Device Zaku II to bolster their military strength, demonstrating opportunistic survival instincts and unwavering dedication to the RPD system, regardless of allegiance.