Around 130 AD, the prosperous and flourishing Roman Empire was under the rule of Hadrian (played by Shinya Tsukamoto). During this time, Roman citizens enjoyed the trend of public bathing, making public baths extremely popular. As the luxury trend rose, bathhouse designer Lucius Modestus (played by Hiroshi Abe), known for his simple and rustic design style, gradually fell out of favor. One day, he accidentally traveled through time via a public bath to 21st century Japan, where he encountered a group of people he referred to as the 'flat-faced tribe.' Their advanced and innovative bathing culture left Lucius both embarrassed and in awe. After this encounter, he traveled through time multiple times, bringing innovative ideas from Japanese baths back to ancient Rome, where he became popular and even caught the attention and favor of Hadrian. During this process, the Hadrian dynasty came to an end, and the seemingly superficial Caionius (played by Kazuki Kitamura) emerged as the new emperor. Lucius refused to design baths for Caionius, and his fate reached a new crossroads... This film is adapted from the manga of the same name by the manga artist Mari Yamazaki.