Kento Mirai is a youth driven by an unwavering passion to become the world's greatest champion in beetle battling, specifically within the Mushiking game. He relentlessly trains with the King of Beetles, Mushiking, dedicating his days to honing his skills for this goal. Mastering the game and proving his ability against powerful opponents consumes his focus.

His path is challenged by the sudden appearance of Shiro Mizorogi, a mysterious boy demonstrating exceptional skill by effortlessly defeating numerous beetle battlers. Shiro wields an unknown beetle, the Dark Side Neptune Beetle, marked by its eerie red eyes and emanating a palpable malevolent aura. This beetle's unnatural power stems directly from Dr. Black, who provides Shiro with dark abilities gained through unethical means solely focused on winning at any cost.

Kento Mirai confronts Shiro and the Dark Side Neptune Beetle, leading to an intense confrontation. This clash pits Kento's dedication and conventional training against the corrupted power Shiro commands. It becomes a pivotal moment highlighting Kento's commitment to the spirit of the sport as he faces an adversary wielding artificially enhanced, malevolent forces.