Thermae Romae Vol. 2 (manga)

Whenever Roman architect Lucius is suddenly submerged in water, he always surfaces to find himself in the land of the “flat-faces,” a people whose appreciation for the public bathhouse matches that of even the mighty Romans! (Little does he realize that the land of his watery journeys is in fact the Japan of 1,500 years in the future!) Observing the strange practices of these foreigners has allowed Lucius to revolutionize the Roman bathhouse, and public opinion on his innovations—and on Aelius Caesar, the emperor-to-be to whom these marvels are attributed—soars. But those in the Senate maintain strong reservations about the suitability of the emperor-to-be, and they mean to cut off the flow of support at its source—Lucius!