A Roman time-traveler discovering that a Japanese stationery store hits the same pleasure center as a public bath is the kind of absurd premise only Thermae Romae pulls off without winking at the camera. Lucius's genuine, unironic joy at finding bath salts and organizational tools operates on the same wavelength as his rapture over ancient plumbing, which means the show trusts you to understand that comfort is comfort across any century. It's a special that gets what made the series work in the first place: taking a silly concept seriously enough that the comedy becomes real.
Lucius ends up at the Japanese chain store called LOFT, where he realizes the fun found in modern-day shopping.