In Vol. 1, we learn that Kazeo's father was part of an archaeological/scientific team investigating the discovery of a giant statue when he became a victim of newly unleashed ancient forces and disappeared. Years later, Kazeo is bullied by other kids in his class and, through a set of circumstances too complicated to explain, winds up in Tokyo just as a special military unit is engaging the aforementioned giant watermelon slice in combat. Again, to make a long story short, Kazeo is endangered and a giant metallic robot emerges from Tokyo Bay to rescue the boy and vanquish the watermelon slice-turned-monster. It's determined that only Kazeo can control the giant robot, which is named Mikazuki, and the head of the secret agency wants Kazeo to work with them, despite his mother's opposition. When the giant watermelon monster returns and attacks Mikazuki, it can do nothing until Kazeo is summoned and gives it orders.
Now, this may all sound pretty ridiculous, but it's done at such a fast pace, with such imaginative (if frequently low-tech) effects and such overwhelming sincerity, that it grows on you pretty quickly. Something new and unpredictable happens every couple of minutes (just wait till you see what kind of monsters the watermelon pits become!), making the 70-minute first chapter (the only part available for review) packed with more clever and cool stuff than an average recent season of "Power Rangers."