Blue Sun Kaiju follows Koji Nakamura, an unfortunate man stuck in an isekai loop. Having died again, he wakes up to find himself in True Nowhere. A white void between all known universes, where the banished celestial Idor has been recycling his soul through each universe he could get his hands on. This collection of universes was turned into DVDs and kept in a disc book.

Idor, took this rare moment as an opportunity and decided to provoke Koji. "If you don't play along as my protagonist, I'll just destroy this universe you called home. Killing your family with it." Now having no choice Koji accepts his reincarnation and becomes the Kaiju protagonist to Idor's newest show. Swearing he will kill Idor to save his family and set free this collected multiverse. In this new universe he meets a kaiju biologist and his psychic daughter, who help him through his journey to kill a deity!