Sweet potatoes are a popular food throughout Japan. They're baked, simmered, added to soup, and turned into confectionery. Baked sweet potatoes are a beloved street food. Recently, sweet potatoes have also been used for purposes other than food. They've been planted on rooftops to keep buildings cool, and waste material from sweet potatoes has been fermented to produce methane for use in generating electricity. We introduce the increasingly diverse ways in which sweet potatoes are used and sold.