Kazuma Harukaze lives a spirited and carefree life on a farm near Mount Fuji with his younger sister Sakura and their horse Lovely. His ordinary existence is disrupted when a meteor-like object hurtles to Earth nearby. This object reveals Hinkle, a messenger from Planet Muzanda, and a robotic horse named Robony. Hinkle delivers a grave warning: King Bull and the Muzanda invaders threaten Earth, aiming to extract its vital Gaia Energy.

To confront this threat, Kazuma transforms into the red-masked hero Devander. He utilizes Robony's unique ability to combine with Lovely, forming the powerful Devander Robo mecha. This mechanized steed becomes his primary weapon. Devander's combat effectiveness relies on an unpredictable targeting system governed by chance rather than precision. During battles, Kazuma occasionally experiences moments of nudity, aligning with the series' comedic tone.

In the final confrontation against King Bull, Sakura provides crucial assistance. Her decisive intervention helps Kazuma overcome the antagonist's forces, securing Earth's safety. With the threat ended, Kazuma returns to his peaceful farm life. This narrative concludes definitively, with no further character development or appearances beyond this single OVA story.