Mr. Mystery is a masked figure and former World BAG Tournament champion. He is consistently identified by his distinctive pink Pac-Man ghost mask. During the second World BAG Tournament's finals, he confronts Fubuki in a Moon Cresta match, though their battle remains unfinished. This encounter leads him to partner with Fubuki in the game "X." After the tournament, he adopts a modified mask featuring the number '2'.

Beyond competition, he mentors Fubuki. He advises her to play no more than one hour daily for peak performance and offers strategic guidance, urging her to improve before the National Finals. He replaces her stolen and destroyed Passion Panties with a new pair. His entrances are characteristically dramatic, often bypassing conventional entryways to crash through Fubuki's window. He is also known for falling flat on his face during his initial appearances at tournaments.

Significant implications link him to Fubuki's past. Moments like Fubuki's reaction to his encouragement during their rematch and his delivery of the replacement Passion Panties strongly suggest he may be Arashi, the individual who originally gave Fubuki the Passion Panties as a child. This potential connection establishes him as a key figure in her gaming development. His motivations appear focused on supporting Fubuki against the tournament's antagonistic forces.