A mysterious letter is delivered to 'Jino', the champion of the Heroes Cup! It's an invitation to the 'Ultimate Watchka Battle League (UWB)', notorious for its ferocity. On the day of the UWB competition, on his way home after watching the match, 'Jino's' Watchka, Bluewill, is kidnapped by unknown assailants. However, after many twists and turns, Bluewill is recovered. Upon discovering the identity of the assailants, 'Jino' decides to hide his own and becomes 'Watchka Mask' to thwart their plot. He then participates in the UWB with Bluewill, transformed into Blue Thunder… Will Watchka Mask emerge as a new hero in the UWB?