I would add that there are two main knife shopping areas in Tokyo. One is in and near the Tsukiji fish market (which is moving soon and is a must see for anyone interested in food) and the other is in the catering supply district across town - about 40 minutes away from the fish market by underground, plus about a 10 minute walk.
There are five specialist knife shops currently in the fish market, and one of these has a larger shop outside. Here is a link to a blog which is pretty informative. I have been meaning to do my own, having been all over Japan and even made knives there, but so far I have not found the time.
My own experience is that Masumoto Tsukiji outside the market is exceptionally helpful and this is in my view the best knife shop in the fish market. I have bought two blue steel and one white steel No 1 knife from there. It is essential that you ask your friend to have the knife sharpened in the shop. if you want a saya (sheath) - and you should certainly get one, this is extra and will need to be asked for. There is also a small charge for boxing the knife and saya. You should pay this too as it makes the knife safer to transport and likely to give you no problems with airport customs. The knife should go in hold luggage obviously. Buy a spare saya pin as well.
Your friend MUST go to the fish market in the morning, preferably early. All the knife shops will be closed by lunchtime.
Incidentally there is also a really excellent book shop in the fish market that has a remarkable range of books. So if you want a book that will show you in superb photographs (don't worry if you don't read Japanese) how to fillet fish, make sashimi, sushi etc then, this is well worth a visit. It is on the corner of one of the shop alleys at the fish market end. Easy to find.
If your friend goes to the Kappabashi catering supply district, there are around a dozen or so shops on the main drag and side streets that either specialise in selling knives or sell a lot of knives with other stuff. One of these is aimed fairly and squarely at the American tourist market and they advertise US speaking ability. This looks like an American shop, with a distinctly western feel inside. Overpriced I thought. Limited brand choice. Avoid.
In this area I like Kamata, which is on the left side of the main street heading north. They were very helpful and have an extensive selection of stainless, VG10, 1 and 2 white, 2 blue etc. The better knives (one piece forged for example) are towards the back of the shop and prices escalate accordingly. They also have about 40 or so decorated knives with fancy sayas if that is your thing. This shop only sells knives. You can get high quality at what I regarded as sensible prices.
Don't expect Japan to be especially cheap. That said, for very high end knives I was able to buy them in Japan for less than half of what I would pay in the UK (if I could even get this quality in the UK).
if your friend goes to Osaka (brilliant) or Kyoto, the choice widens, but you will easily get fine quality in Tokyo.