"Dual! Parallel Trouble Adventures Special" is a six-episode OVA series that serves as a condensed retelling of the original 1999 TV anime "Dual! Parallel Trouble Adventure." The story revolves around Kazuki Yotsuga, a high school student who becomes entangled in a conflict between two parallel worlds. Kazuki is a socially awkward but mechanically gifted individual who spends his time building robots in his garage. His life takes a dramatic turn when he encounters Mitsuki Sanada, a mysterious girl who claims to be from a parallel universe.

Mitsuki explains that her world, known as the "Second World," is at war with the "First World," the reality Kazuki inhabits. The Second World is technologically advanced, with giant mechs called "Parallel Robots" being a central element of their military strategy. Mitsuki is a pilot of one such robot and seeks Kazuki's help to prevent the destruction of both worlds. Kazuki is initially skeptical but is forced to confront the reality of the situation when he is transported to the Second World and discovers his own latent ability to pilot Parallel Robots.

In the Second World, Kazuki encounters a cast of characters, including D, a scientist who created the Parallel Robots, and Ayuko, a childhood friend who is revealed to have ties to the conflict. The narrative explores themes of duality, as characters from both worlds have counterparts with differing personalities and roles. Kazuki's journey involves navigating the complexities of these parallel realities, uncovering the truth behind the war, and reconciling his own identity across both worlds.

The plot is driven by a series of battles between Parallel Robots, with Kazuki gradually mastering his piloting skills and forming alliances with key figures in the Second World. The conflict escalates as the true motives of the war's instigators are revealed, including the involvement of a powerful entity known as the "Absolute Guardian." Kazuki must confront this entity to prevent the collapse of both worlds, leading to a climactic showdown that tests his resolve and ingenuity.

The OVA condenses the original series' storyline, focusing on the core narrative elements while streamlining character development and subplots. Despite its shorter runtime, it retains the original's blend of mecha action, science fiction, and lighthearted humor. The series concludes with Kazuki and his allies achieving a resolution that ensures the survival of both worlds, though not without sacrifices and personal growth along the way.