Nobita and his friends go on a sea adventure as part of a spring break request, with Doraemon using a gadget to create a “moderate” treasure island experience. They are guided by a dolphin-like robot named Hodho, but the adventure turns strange when the treasure they find is just merchandise instead of real riches. After Gian and Suneo complain, Doraemon increases the difficulty, leading to real danger: storms, malfunctioning gadgets, and transformations into sea creatures to survive. The group eventually discovers the true treasure inside a whale, but the adventure keeps shifting between too easy and too hard, leaving them confused as Hodho insists everything is “just right.”