I went to Gyoza Tengoku (Gyoza Heaven or Gyoza Paradise or whatever) on Friday with friend. It was first time I had big gyoza, I enjoyed it very much! Of course I had chuhi too, it plused my happiness.
We ordered cheese, vege and shrimp. All of them were good. I want to try garlic sometime, but maybe everybody on way to home will hate me. heh.It is located about 7mins from Tachikawa station. English menu is available.
you can see duty hour here. http://www.geocities.jp/gyoza1059/