"Moldiver" is a six-episode OVA series set in a futuristic Tokyo where advanced technology has become an integral part of daily life. The story centers around Hiroshi Ozora, a brilliant but socially awkward scientist, and his younger sister, Mirai Ozora, a cheerful and energetic high school student. Hiroshi has developed a revolutionary powered suit called the "Moldiver," designed to enhance human abilities and grant superhuman strength. The suit is intended for use in construction and other industrial applications, but its potential for combat becomes apparent when it falls into the wrong hands.

Mirai, curious and impulsive, accidentally activates the Moldiver suit during one of Hiroshi's experiments. The suit bonds with her, granting her incredible powers but also locking her into its form, making it impossible to remove. This unexpected turn of events forces Mirai to take on the role of a superhero, using the Moldiver suit to combat a group of rogue scientists and criminals who seek to exploit the technology for their own gain. The antagonists, led by the enigmatic Dr. Tokita, aim to use the Moldiver's capabilities to dominate society, creating a series of escalating conflicts.

As Mirai adjusts to her new role, she faces challenges both in and out of the suit. Her inexperience and lack of training often lead to comedic mishaps, but her determination and resourcefulness help her grow into her responsibilities. Hiroshi, meanwhile, struggles to regain control of the situation, working tirelessly to find a way to remove the suit from Mirai while also supporting her in her battles. The siblings' relationship evolves as they navigate the dangers and responsibilities brought on by the Moldiver, with Hiroshi's technical expertise complementing Mirai's bravery and adaptability.

The series blends action, comedy, and science fiction, exploring themes of technological advancement, ethical responsibility, and the unintended consequences of innovation. The narrative is driven by Mirai's transformation from an ordinary teenager to an unlikely hero, juxtaposed with Hiroshi's efforts to mitigate the risks posed by his creation. The dynamic between the siblings, along with the colorful cast of supporting characters, adds depth to the story, creating a balance between lighthearted moments and high-stakes action. The OVA concludes with a resolution to the immediate conflict, though it leaves room for further exploration of the Moldiver's potential and its impact on the world.