The second season of the mini series starring the girls of BanG Dream!

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.

In the hollow Mysterious Planet, seven kingdoms co-exist, all of them lit by the Sun's Blessing from the Kingdom of the Sun, in the middle of the planet. The light of the core sun is necessary for the continued existence of all the kingdoms. Yet, something is causing the Sun's Blessing to weaken. If something isn't done, it will be the end of life in the Mysterious Planet. Fortunately, the twin princesses of the Sun Kingdom, Fine and Rein, have been endowed with the magic of the Prominence, and are looking for a way to fix things. (Source: ANN)