In a clandestine underground auction, the coveted Mermaid's Scale, a precious Aquamarine gem, emerges. The notorious underworld queen, known as the 'Bearslayer,' manipulates the skilled thief Lupin to purloin the jewel for her. Lupin successfully steals the gem, only to realize it's a fake, unraveling a profound secret: the authentic Mermaid's Scale holds the key to defying death itself. As chaos ensues, the 'Bearslayer' meets a brutal demise, sparking a chain of events where her enigmatic young assistant, Misa, is abducted by the arms dealer Himuro. Now, Lupin and his crew must race against time to unlock the mysteries of eternal life before it falls into the wrong hands and plunges the world into unending conflict.