Continuation of Teppei's journey with B't X to rescue his brother Kotaro Takamiya from the Machine Empire. The OAV series picks off from the TV series from the point where Hokuto successfully saves both Teppei and B't X and makes B't X far more powerful than before. (Source: ANN)

Teppei is going to visit his older brother Kotaro Takamiya during a scientific conference after training with a mysterious woman named Karen for the past 11 years. However his plans for a family reunion become stalled when a woman named Aramis kills everyone in the conference to kidnap Kotaro. Teppei on the way to save his brother encounters a broken mechanical horse called B't X who revives thanks to Teppei's blood and is now his aide to save his brother from the mysterious Machine Empire.

Based on the American cartoon, "The Powerpuff Girls." Professor Utonium and his son Ken are studying the strange Chemical X. When a mochi cake falls into the formula, it changes into Chemical Z. Ken fires a ray of Chemical Z at a glacier in Tokyo Bay, however that causes strange black and white lights to scatter. The black lights turn its victims into monsters, with emphasis on a black light hitting a zoo monkey and transforming him into Mojo Jojo. The white lights, however, aim at three normal girls, Momoko, Miyako, and Kaoru. This gives them the power to transform into superheroes, the Powerpuff Girls Z!

On the run from the Erste Empire, Gran and the crew of the Grandcypher receive an offer to negotiate a ceasefire. Meeting at the neutral territory of Albion Citadel, they are welcomed and hosted by Vira Lillie: current Lord Commander of Albion and a friend of Katalina Alize from her officer training at Albion. Imperial General Furias grants the Skyfarers an official pardon, but fails to defuse the tense situation. Given time to unwind, the Skyfarers attend a gala hosted by Vira to celebrate the arrival of the crew. However, tensions run high, as Furias and the Erste delegation remain at Albion even after the negotiations conclude. Learning about the existence of a Primal Beast on the island, the crew is shocked to discover a letter from Katalina announcing her resignation. While Gran heads off to find their former comrade, Eugen and Rackam decide to investigate the Imperial presence on the island, suspecting a more sinister scheme lying up the Empire's sleeve. [Written by MAL Rewrite]