The series follows a Japanese schoolboy, Koichi, who learns that he is the reincarnation of the alien entity, Babel. As such, Koichi is entrusted with Babel's powers and joined by three protectors: Rodem, a shape-shifter usually taking the form of a blond princess on standby then a black panther when combat ready; Ropross, a pterodactyl-like flying creature; and Poseidon, a giant robot that always rises from the depth of the ocean when summoned. There's also a 5,000 year old computer providing helpful information at the tower, totaling four entities ("three servants"). The boy hero commands his newfound powers and companions in order to defend the Earth - specifically, under his inherited role, he is destined to meet up with Yomi - "the man who will either become his best friend or greatest enemy", thus triggering a long rivalric battle to essentially remove the other from the picture in a sort of war for supremacy.