BSX-3, officially designated Mega Diver, is a specialized Battle Skipper developed by Uruyasu Heavy Industries for the Exstars team. Primarily an underwater attack unit, it is piloted by Saori Tachibana. The mecha is painted in a blue color scheme and shares common Exstar specifications: an estimated height of 4 meters, weight of 2 tons, and a combined turbofan jet engine with high-mobility organic motor delivering 2,500 horsepower. Its armor is fortified with composite space material for enhanced durability.

Mega Diver excels in aquatic environments, achieving a swimming speed of 200 km/h. Key equipment includes a hybrid-bullet recoilless gun for ranged combat. A signature feature is its integrated AIES (Artificial Intelligent Expert System), enabling an auto-combat mode that executes specialized martial arts techniques. The AIES software offers selectable combat disciplines: Taekwondo, Bajiquan, Muay Thai, and Gracie Jiu-Jitsu for enhanced close-quarters combat.

Across the OVA episodes, Mega Diver engages in multiple critical missions. During conflicts involving Todou's hypnotic manipulation of Saori, the mecha participates in combat sequences culminating in the destruction of the Exstars' initial base. In the final confrontation against the Debutante Club's forces, Mega Diver operates from the mobile fortress Josephine Rose, contributing to the defense against Makuhari Heavy Industries' flying fortress. Its combat capabilities and Saori's synchronization with the AIES system aid in repelling antagonists and protecting the Etiquette Club's interests.