Mid Previa is the grandson of the renowned inventor Cid Previa, also known as Shido. He appears in the anime as a ghost, having been killed two hundred years before the events of the story. During his lifetime, Mid and his grandfather were scholars who helped guide the four Warriors of the Crystals to victory over the villain Exodes. After the war, Cid died of exhaustion, and as Mid prayed at his grandfather's grave, the wizard Ra Devil exhumed Cid's body and stole his brain. Mid protested and was killed for his resistance. Unable to find peace due to the torment over his grandfather's fate, Mid's spirit took refuge within the Wind Crystal. When the new heroes—Prettz, Linaly, Valkus, and Rouge—encounter the crystal, Mid's memory of his death is revealed to them. Later, he emerges from the crystal to assist them in person.

Mid is intelligent and studious, having inherited his grandfather's passion for engineering and invention. He idolized Cid and aspired to become a great inventor himself. His primary motivation is to free his grandfather’s spirit from the clutches of Ra Devil, who is using Cid's knowledge to awaken the destructive power of the Void, Deathgyunos. To this end, he aids the protagonists with his deep knowledge of history, the crystals, and the events of the past. His role in the story is that of a guide and informant, providing crucial context and advice. He also forms a subtle romantic attachment to Linaly, which creates a playful rivalry with the hot-headed Prettz, though Mid generally responds to Prettz’s jealousy with patience and calm. Despite his ghostly nature, he remains earnest and helpful, and his presence is key to unraveling the villain’s plans. His notable abilities include his encyclopedic recall of historical facts, his understanding of crystalline energies, and his capacity to manifest and communicate even after death. A boy with short blonde hair and black eyes, Mid is a childlike spirit whose unresolved grief drives him to see the story through to a peaceful conclusion.