freecia's account has reminded me of another scenario. I got talked into attending a large Japanese cultural event in London a few months ago and amongst the assorted events was an introductory tea ceremony.
One of the volunteers was a lady who had looked very chic in her adaptation of 20s era Japanese clothing in the Western setting of the events hall. The moment she discarded some of her accessories and climbed onto the prepared tatami (a space rarefied by the presence of artfully placed tea ceremony artefacts) she changed completely. Her collar gaped open over her cleavage, and the lower hem of her kimono, arranged high to accommodate a pair of fetching boots, yawned wide over bare legs. The lady appeared oblivious to all of this and seemed to be trying hard to appear dainty and refined with her gestures. My husband physically blushed and, when prodded, whispered “onsen geisha” to me. I knew exactly what he meant.
Perhaps it was the juxtaposition of the modern getup in the traditional setting but the effect was peculiarly sordid (like going to Fortnum & Masons for tea and seeing someone in hotpants, a bikini top and a permatan at the next table). In contrast, my mother, a proud stranger to fashion and with no affectations of elegance of manners, had also volunteered. She looked serene and composed in a turtleneck and slacks with a wide armed haori jacket thrown over the top.

Undergarments under Japanese clothes are most definitely a good idea.