Amago Tsunehisa transfers into a daycare and makes friends with a boy named Shimizu, who decides to help fulfil her dream of building a large sandcastle in the sandbox. Tsunehisa starts using her wisdom to slowly gain control of the various territories of the sandbox. However, another classmate named Misawa tells on the teacher, who forbids Tsunehisa from using the sandbox until after the weekend. The next week, Tsunehisa attempts negotiations with Misawa over how to split turns on the sandbox, but ultimately fails...