Marine Boy also has a friend in Neptina, a young (8-12-year-old?) bare-chested mermaid who was always kept decent by her long flowing hair. Neptina wears a magic pearl around her neck, which could be used for various purposes including creating an envelope of protection and deterring dangerous animals (episode 1, 2, 17), as well as working as a crystal ball to see events (ep. 3, 6, 13, 15, 16, 17). She also seems to understand Splasher (ep. 3, 6, 10) and have an innate understanding of sea life (ep. 4). During battle Marine Boy always directs her to safely stay out of harm's way, and Neptina always submits, then almost inevitably ends up saving Marine Boy. However, in spite of all his gadgets, Marine Boy is knocked out several times by the villains. Marine Boy often faints after being attacked with knock-out gas but Marine Boy is also knocked unconscious by robot spiders, red dolphins and mysterious seaweed, to name but a few. He is also frequently kidnapped by the villains but usually rescued by his friends.