If you look at photos of Tokyo apartments from the early '90s (eg _Tokyo: A Certain Style_, https://www.gwern.net/docs/japanese/1997-tsuzuki-tokyoacerta... ), which were often photos of people making very similar tradeoffs for the same reasons (cheaper rent in the heart of Tokyo but then-relatively-small apartments, often one-room), the apartments are much larger than these but also far more cluttered, looking like they have hoarding disorders. Stereo sets, TVs, landline phones, walls or giant stacks of manga, vinyl records, cassette tapes, reference books, books in general, musical instruments (he photographed some musicians and music students), visual arts equipment - all of these take up an enormous amount of space collectively. But they can all be replaced by a desktop+large monitor and a smartphone and perhaps a digital input device like a tablet or keyboard for arts. (Even the desktop is physically far smaller than in the '90s.)
And that's precisely what the photographed apartments here do: you see desktop computers, a small handful of books which perhaps are sentimental or favorites, and much of the bulk of the space seems to now be used up by clothes, with food-related items being the next biggest category.
This raises the question of what could be done to reduce those? Food patterns will probably shift further to takeout/online purchases because of the enormous investments in logistics for rapid delivery (I'm particularly impressed when I read about JD.com in China, and Tokyo is a logical megalopolis to reach similar delivery speeds), but clothes are a tougher nut to crack. New fabrics which are more dirt/odor-resistant to allow more wear? Reversible clothes which provide '2 in 1'? Fewer dresses and more mix-and-match? Rental clothing services powered by cheap delivery?