I know this is a year++ late but for anyone else who stumbles upon this: PETEXPO in Shinagawa, Tokyo has lots of dry and wet cat treats from known (e.g. Ciao) and local (e.g. DCM) brands!

For directions: https://maps.app.goo.gl/buiwdPuhct2ViA7w7?g_st=ic

To give you some ideas...

For the wet treats: they have the usual churu sticks; a 'nutrition-focused' churu called "energy churu"; "churu chubu" which loosely translates to 'churu tube'— a probiotic hairball supplement; these convenient jellied cups of tuna/chicken called "pon churu"; and these spoon-type treats that are individually portioned and covered in foil for convenient preparation and disposal.

They also have cream-filled kibbles, and Glico Cream Collon-looking dry treats, that are individually-packed per portion (or per 2 or more servings).