Hi Jan, it will work in fact in the Tokyo (Kanto) area, Mentsuyu is made with darker soy sauce. Usukuchi is primarily used in the Kansai region (Osaka/Kyoto) and produces a lighter colored broth. One thing to be aware of is that Usukuchi has a higher salinity than regular dark soy sauce, but as long as you're aware of that when you dilute this, you shouldn't need to change the recipe.

Hi Marc, I can't find the soy sauce Usukichi but have Kikkomen Traditional soy sauce. Is it okay to substitute? I can purchase Shoyu here also.

Hi Rebekah, for cooking you don't need to use a fancy sake since most of the more delicate nuances will evaporate. Some common brands available in the US are Hakutsuru and Sho Chiku Bai, but whatever you can find should work. Just be sure to avoid "cooking sake" as they almost always include salt and preservatives which will throw off the taste of any recipe.

What brand of sake do you recommend? And, is there an online store where I can buy the sake in the US? Thank you!