The story unfolds in the worldview of multiverse theory, where there is not just one universe. In the overlapping multiverses labelled as "Cosmo Layers", there exist other Earths that are identical to the Earth we live on. Gavan Infinity is a Space Sheriff who can transcend dimensions. What kind of cases will he solve in the diverse dimensions he is set in, and why can he transcend dimensions? A new Gavan legend never before seen begins!
Reiji Doki, an investigator for the Galaxy Federal Police, is Gavan Infinity—the sole individual in the cosmos authorized to bear the title "Space Sheriff Gavan." Yet he languishes in the marginal Records Division, enduring daily ridicule from detectives in the Criminal Investigation Division. Few know his true purpose: investigating transdimensional Emorgear crimes. Reiji now heads for "Multiverse Earth Λ8018," where an Emorgy Negative Wave threatens to expand across dimensions and potentially collapse the entire universe. Amidst Λ8018's chaos, he encounters Setsuna Aikokuin, captain of the Galaxy Federal Police's Special Forces Unit...!
Setsuna, known as Gavan Bushido, the Space Sheriff Gavan of MultiEarth Λ8018, confronts Reiji, who has fused with Gavan—a being that shouldn't exist in two forms... To silence the arrested Hitoshi Kuzumi, the crime syndicate's boss, Karasumaro, attacks Setsuna and his team. As one incident follows another, Setsuna sees Reiji burning with rage toward Karasumaro and...!
Reiji, pursuing a new Emorgear negative wave, heads to MultiEarth Ι5109. There, he begins investigating an Emorgear incident where humans turn into bubbles, alongside the duo of Kiki Iwai and Kotobuki Takanari from the Galaxy Federal Police's Forensics Division.
As the trio sought the truth behind the incidents, a new Emons attacked them, and Kiki transforms into Gavan Luminous!
On MultiEarth Σ3302, a series of bizarre incidents occur where vital facilities vanish one after another! Reiji, dispatched to the scene, encounters the Galaxy Federal Police investigative duo: Mikuro Arimoto and Shoko Hamura. Though shocked by Arimoto's seemingly impossible existence, Reiji begins investigating alongside them.
Soon, Reiji and his team arrive at a mysterious underground fortress, only to be attacked by the culprit's drill machine and find themselves in a pinch...!
Setsuna and Peacekeeping Corps Chief Rui Amou were racing to arrest the smugglers conducting clandestine deals on MultiEarth Λ8018. Amidst this, Amou was abducted by an unknown assailant. Though every moment counted, Headquarters orders Setsuna to stand by...
Conflicted, Setsuna reunites with Reiji, who has crossed dimensions, and is entrusted with something. As the two fight together once more, the secret behind Setsuna's dual-wielding style is revealed...!?