Once upon a time, this world was created and destroyed by a single girl. The ones who saved the girl's heart were Hyper Agent Gridman, who appeared from another dimension, a monster with a heart created by the girl, and high school student Yuta Hibiki. Yuta, who has advanced to the second year of high school, decides to confess to Rikka, who is in a different class. However, their peaceful daily lives are shattered by the sudden appearance of a monster. Gridman reappears in front of Yuta and tells him that the balance of this world is about to collapse. Eventually, the crimson dragon Dynax, Gridman's supporter New Century junior high school student, and Yomogi Asanaka, a resident of another world, appear, and Yuta gets caught up in an extraordinary situation.