Mr. Cash (Ｍｒ. キャッシュ Mr. Kyasshu) is the main antagonist of the movie Nobita's Great Adventure in the South Seas. He is an evil villain who experiments with (and ultimately, kills) innocent animals, capturing them and making abnormal animal hybrids to earn money.
Mr.Cash worked together with Doctor Clone, a scientist that was banished from the 22nd century council for cloning and creating illegal hybrid creatures, in order to sell them and gain a huge sum of money. Using Tomos Island as his base of operation, Mr.Cash had his men capture a large amount of pirates that came to search for the treasure on the island with Captain Cole and his crew among them. In order to prevent the Time Police from discovering his plan, Cash used the secret passage within the island and installed the Loop Barrier that prevented the Time Police's sensor from locating their base of operation. He also used a giant sea dragon "Leviathan" as a final guardian and weapon should anything go wrong.
When Doraemon and his friends, along with Captain Kid and his crew and Captain Cole's daughter Betty came to the island to search for Nobita and Jack, Betty's younger brother, Cash used a 22nd Century Virtual Game gadget to trap them and eventually capture the entire group, except Pancho and Gonzales who went through the other path. Later, he had his men capture Nobita, Jack, and Luffin who wandered into the underground area through the waterway. After revealing his goal and identity to all of them, Cash taunted Doraemon and had everyone locked away, separating Luffin from the rest in order to use him to create Dolphin-Crab monster hybrid. However, Pancho and Gonzales managed to free the group from their imprisonment and eventually located and rescued Luffin, along with Captain Cole and his crews from the underground prison.
Enraged that his plan had failed, Cash decided to transport all the hybrids to his escape ship and summoned Leviathan to deal with his enemies. However, Cash's control over the beast was thwarted by Doraemon and Nobita who attacked the control tower in order to disable the Loop Barrier and caused the control room to fall down from the mountain onto the ship. Cash and Doraemon were then swallowed by Leviathan. Left with no choice, Cash attempted to bribe Doraemon into helping him get out of the beast's belly which Doraemon refused (as he can safely leave Leviathan's body through its digestive tract without having to fear its gastric juice). Unexpectedly, they're rescued by the Dream Tester with it pinching Leviathan's stomach, causing the beast to vomit the two of them out. Cash, along with Dr.Clone and his goons were then arrested by the Time Police.