Masaru Aso was originally an assistant to Doctor Mochizuki until the doctor conducted experiments on him. Horrified at being made into a grasshopper-like cyborg, Masaru went into hiding in the mountains for two years until he awoke with an unconscious urge to protect Hiroshi. Though he hated Mochizuki, Masaru eventually forgave him before learning the man was telepathically communicating with him.