Namako-Otoko, alternatively called Sea Slugman or Mr. Sea Cucumber, originally operated among Takeshi Onimaru’s demon forces under the antagonist’s command. During an assignment in Izu, he separated from his unit and encountered Yaiba Kurogane’s group, prompting his immediate defection from Onimaru and permanent allegiance to Yaiba’s team. Post-defection, he remained a steadfast ally, often observed perching on Sayaka Mine’s shoulder. His dialogue consistently concludes with the distinct verbal tic "Zura" (ズラ) across all official portrayals. Retaining aquatic, mollusk-like physical traits reflective of his sea cucumber namesake, he contributes minimally in combat but serves as a supportive and intermittently comedic element within the group dynamic. His background aligns him with other Onimaru-summoned defectors like the frog demon Gerozaemon Geroda. His character arc centers on adapting to ally status, bolstering group unity without instigating major plot developments. Following Onimaru’s defeat and the dissipation of mystical energies at the series’ conclusion, Namako-Otoko—alongside Gerozaemon—reverted to an ordinary animal form. Both resided in the Mine family’s backyard pond during the epilogue, set three years post-main events.