Sweet vinegar: "Amazu" 甘酢 can be made ahead. It keeps a long time in the refrigerator. I put the aforementioned rice vinegar (it was about 1 and a half cups) in a non-reactive (such as stainless steel or Pyrex) pan on low flame and added sugar (half the amount of vinegar, either by volume or weight) and a small amount (I used 1/2 tsp but could be more) salt. Stir and make sure the sugar is completely dissolved and let it come to boil (called "nikiru" 煮きる), this makes the vinegar mellow. Let it cool down and put it in a plastic or glass container and keep it in the refrigerator. This can be used for many other recipes.
Marinade: I use 2/3 cup of sweet vinegar for one chicken breast. I add dashi (1/4 cup), mirin and soy sauce (1 tbs each). Put it in a sealable flat container to be ready for receiving the chicken.
Chicken: I make thin bite size pieces from one skinless, boneless breast by cutting across the grain of the meat on a slant. I season it with soy sauce and grated ginger (just enough to coat the meat pieces but no extra liquid should remain) and coat each piece of meat by mixing by hand and let it sit for 10-15 minutes at room temperature.
Dredging: I use potato starch or katakurko 片栗粉. This creates a nice even crust which does not come off easily and also produces a nice slippery surface after the cooked chicken is soaked in the vinegar marinade.
Frying: I again used shallow frying at 170C (340F). Since the meat is thin, it takes 1-2 minutes on each side and comes out very crispy but meat becomes kind of dry but that is OK. It is good to eat as is (which we did). It is quite different from the chicken thigh tatsutaage 竜田揚げ and it is very good in its own right.
Marinating: While the chicken pieces are still hot, add them to the sweet vinegar marinade. I also add thinly sliced red onion, julienned carrot, and red pepper flakes. You should add as much vegetables as you like or the marinade can accommodate. They are very good after pickling. I marinade them at least overnight or longer in the refrigerator.
The end result is quite nice. It is a very interesting melding of flavors. The frying cuts the acid of the sweet vinegar and the vinegar cuts the oiliness of the frying. The result is a refreshing dish with real depth. In addition, over time the chicken picks up the flavor of the vegetables with which it is sharing the marinade. The texture of the chicken is nice because the crust from the frying is still intact but develops a nice slippery or smooth surface (but not slimy, for those who have slime-o-phobia). The pickled vegetables are a nice accompaniment. Beer or sake may be a safer pairing but we had this with a Cali cab, Louis.M.Martini Cab Sauv, Alexander valley, Reserve 2007*. This wine has a nice earthy overtone with good firm tannin and went surprisingly well with this dish. The acid in this dish appears not to compete with this wine.
*P.S. Even after it was bought out by Gallo, Louise.M.Martini keeps making reasonably priced good quality wines, we liked their Napa cab and this reserve from Alexander valley (regular cab from Sonoma is so-so). Ghost pine, which is one of the Gallo's numerous brands but made by L.Martini, is also good.