Battsu, also known as the Demon Lord Dragon, is a forbidden monster originating from Dragon World. Sealed within an ancient shrine after devastating the continent, Battsu possesses a tyrannical and initially uncontrollable nature, disregarding authority and exhibiting destructive tendencies. This imprisonment lasted until Gao Mikado accidentally broke the seal during a visit to Dragon World. Despite Battsu's history of devastation and resistance to forming bonds, Gao persists in seeking a partnership. This leads to Battsu becoming Gao's primary Buddy Monster, replacing previous partners like Drum Bunker Dragon and Bal Dragon. Their relationship evolves from mutual distrust to a deep bond, marked by the pivotal "Starry Sky Promise" signifying Battsu's growing loyalty and emotional connection to Gao. Throughout their adventures, Battsu undergoes significant transformations. He achieves the "Overturn" ability, evolving into Overturn Black Death Dragon during a confrontation with Wisdom's forces, representing a critical development in his capabilities. Battsu's combat style remains aggressive and overwhelming, leveraging immense dragon strength and dark energy attacks aligned with his Demon Lord heritage. A major turning point occurs when Battsu and Gao experience temporary separation during a conflict, highlighted by the episode "Buddy Breakup! Farewell, Batzz!". This separation tests their bond but ultimately reinforces their commitment. Battsu later participates alongside Gao in the Gao Genuine Gameface Tournament during the "All-Star Fight" arc, competing against other renowned fighters and monsters. In the GGG Cup, Battsu's presence proves integral to Gao's strategies. Their teamwork culminates in high-stakes matches, including a notable showdown against Tasuku Ryuenji. The tournament showcases Battsu's full integration into Gao's life and the broader Buddyfighting community. Battsu's journey concludes with the final episode of "All-Star Fight," where his partnership with Gao remains solidified.