Ancient Roman architect Lucius is too serious. His inability to keep up with the fast-moving times costs him his job. When a friend takes the dejected Lucius to the public bathhouse to cheer him up, Lucius accidentally slips through time and resurfaces in a modern-day public bath in Japan. There, he meets aspiring young manga artist Mami, along with others of the "flat-faced clan". Shocked by the many inventive aspects of Japan's bathing culture, Lucius returns to ancient Rome and garners tremendous attention when he implements these novel ideas back in Rome. As he time-slips back and forth between ancient Rome and modern-day Japan, Lucius' reputation as the ingenious, new bath architect begins to grow.