Geo is a young protagonist who styles himself the "Master of Survival," though luck often plays as significant a role as his bold actions. He is friends with Phoebe and interacts with the eccentric scientist Dr. Brain and Dr. Brain's assistant, Kay. The core narrative begins when Geo visits Phoebe and Dr. Brain, resulting in him and Dr. Brain accidentally being swallowed inside the microscopic ship SS Hippocrates within Phoebe. Trapped inside her body, Geo must rely on adaptability and courage throughout their perilous journey across her internal systems. He confronts challenges like battling Helicobacter pylori bacteria in the stomach using the ship's lasers and pursuing parasitic hookworms in the small intestine. His survival instincts are constantly tested, from evading digestive processes to navigating the hazards of the circulatory system.

Traveling through the digestive system from mouth to rectum, Geo and Dr. Brain face near-excretion before being reabsorbed by villi in the large intestine. They transition to the circulatory system, experiencing the heart's powerful pumping and the liver's processing. Later, within the nervous system, their movements inadvertently interfere with Phoebe's motor functions and speech. Geo evolves from observer to active participant, crucially aiding in the discovery and ultrasound elimination of a brain tumor. The 2020 anime film adaptation follows this storyline closely, depicting Geo swallowed aboard the Hippocrates during Phoebe's snack and journeying through her bodily systems without adding new character elements. His portrayal remains consistent as a resourceful and determined figure navigating internal bodily environments alongside Dr. Brain.