 Goemon encounters Nezumi-Koozoo IV(Ratboy Jirokichi IV) the fourth decedent of a great thief. He tells Goemon that their ancestors teamed up at the International Thieves  Championship. But they were defeated by Lupin s grandfather Arsene Lupin the 1st. Ratboy suggests Goemon that they should team up and avenge their ancestor s dishonor. And to do that they ll beat Lupin by stealing secret data from the Sakurada Police Station before Lupin gets the chance in nabbing it.