Dr. Koutaro Azuma created Android BK-1 to protect the earth. In following its final directive, to protect the environment, BK-1 determined that humanity was a threat to earth. Renaming itself Black King Boss, BK-1 created an army, the Andro Corps, to destroy all human life. As humanity falters, Tetsuya, son of Dr. Azuma, initiates his father's last experiment to create the ultimate android. He Merges himself with the machine, and creates Casshan the symbiosis of humanity and machine. Casshan has one single goal, to eradicate the Iron Evil, Black King Boss. Casshan travels with an advanced transforming robotic dog named Friender. Friender is as much a fighting assistant as an affectation to replace Tetsuya's dog, Lucky. While trying to reach BK-1 Casshan encounters human resistance member Luna Kouzuki. Luna possesses a weapon capable of defeating the Andro Cops, and she is trying to get it back to the human army. She has also been searching for Tetsuya while fighting the robot army. When they finally meet, she is faced with the fact that Tetsuya is dead while Casshan confesses to her his fear of becoming another BK-1. With humanity's future on the line and Casshan's humanity slipping away will he be able to defeat BK-1 or will he join his BK-1's army in the end?