Bundled with the fifth manga volume.

All Rumi Yokoi wants to do is focus during school, but she is constantly distracted by Toshinari Seki, her neighboring classmate. Paying attention during class is the least of Seki’s worries, as he obsesses over intricate setups created using an assortment of items, from an elaborate domino course on his desk to a treacherous war […]

He was the king of the demon world that had been laid off because of complaints. She was the hero that had lost her position because she failed in her crusade. Fate bound these two together, and they began a journey filled with mysteries and to pay off their debts.

The Bladebreakers have to join forces once again because a mysterious group under the lead of Oozuma has defeated them, but the real enemy is not Oozuma. The real threath is formed by a group of people who use cyber-BitBeasts to capture the original ones from the Bladebreakers. (Source: ANN)