If you're over 80 kg, buying clothes here will be fairly difficult, although others have pointed out acceptable stores. If you're under 80 kg and not overly tall (I'm ~195 cm and ~80 kg), you shouldn't have too much trouble. Shoes will be a big problem if you have big feet (whenever I go somewhere that requires slippers, I bring my own). Uniqlo should have acceptable clothing, although be sure to try things on. Fits can be quite different here, even if the sizes are technically the same. There are some Gaps and there should be J Crew in Tokyo too.