Thermae Romae is a Japanese movie directed by Hideki Takeuchi and based on a manga by Mari Yamazaki.
See also: Thermae Romae 2 (2014)
An ancient Roman bath house architect named Lucious loses his job due to his inability to keep up with the times. When his friend takes him to a public bath house to cheer him up, Lucious slips forward through time while desperately seeking inspiration for a new idea and winds up in a present-day bath house in Japan.
In Japan he meets a young aspiring manga artist named Mami and other Japanese people who he refers to as the “flat-faced clan”. Lucious is fascinated by Japan’s modern bathing culture, and bounces back and forth through time to implement these advancements in ancient Rome while establishing his historical legacy as a genius inventor.