Soul Diver was one of Kururu's inventions. In the 64th episode the soul diver made Keroro, Giroro, and Tamama to enter Dororo's mind and fix what is wrong beacuse Dororo was haveing trauma problem that will stay this way permanently. What the Soul Diver do is it put Keroro, Giroro and Tamama in the ball Dororo was in that will make them go in Dororo's head that will go to his memories.
Another appeared in the anime where Keroro Platoon and Pururu enters inside Giroro's memories. But it seems Kururu is enjoying of tweaking Giroro's memories such as changing love of Natsumi into love of Kururu or changing Natsumi's face into Kururu's, which made Giroro shrieks in panic as he goes out of control and destroyed the Soul Diver. Pururu mentioned Kururu likes Giroro in the end of the episode.