The picture below is what I cooked. The closest skewer is Yuzu-koshou and Jalapeño pepper, the middle is sweet miso with "shiso" しそ perilla and the furthermost with onion is with a "tare" sauce.
I. "Tare" or "Tsume" sauce たれ or つめ (right in the picture below).
Many "Yakitori" places have their secret sauce which has been in use for many years. The sauce is maintained by straining the old sauce, adding a new batch and cooking it again everyday. Dipping grilled chicken into it everyday for many years, of course adds to the flavors. Home cooks could not possibly match this.
Another similar sauce is called "Tsume" which is a short for “Tsume-dare” つめだれ. “Tsume” comes from the word "nitsumeru" 煮詰める or to "reduce" by boiling. It is usually used to "paint" some sushi like "anago" 穴子. It is essentially a concentrated ”sweet and salty” or “ama-kara” 甘辛 sauce made from soy sauce (mirin, sake) and sugar with some savory elements (classically, for anago, I was told, grilled "anago" bones were used. Some recipes use pre-made “oyster sauce”).
Mine started out as the simmering liquid for "Vermillion snapper". After the fish was cooked and removed, the remaining and reduced seasoning liquid totally congealed in the refrigerator because of the protein components from the fish. I diluted this using “dashi broth” and made a simmered tofu or “Niyakko” 煮奴. After making this dish, what remained of the simmering liquid was kept in the refrigerator. This was the base of the sauce I used here. I tasted the sauce and added more soy sauce, mirin and reduced it to 1/3. It became slightly thick and tasted salty and sweet (not as sweet as some Yakitori “tare” sauce) with good savory “umami” flavors (right in the picture below). Of course, you can make this sauce simply by mixing soy sauce, mirin or sugar and thickening it with a potato starch slurry.
2. Sweet miso with perilla 大葉入り甘味噌 (left front in the picture above).
This is made with miso (2tbs), green perilla (2 large leaves finely chopped), and mirin (about 2 tbs or until the consistency of the miso reaches a saucy stage). I thought of adding a bit of dark sesame oil but refrained.
3. Yuzu-koshou and Jalapeño pepper 柚子胡椒ハロペニョ (left back in the picture above).
I made the least amount since this was rather spicy. I finely chopped up half a Jalapeño pepper (1/2, seeded and deveined) and mixed with yuzu-koshou (1 tbs) and mixed in mirin (1 tbs). I was thinking of adding lemon zest (micrograted) but forgot to do it.
I boned and skinned 6 thighs (3 were large but three were small). I cut them into a bite size chunks. I just made 4 skewers just from the chicken and two with sweet onion (left in the picture below).
Since I had to use more skewers than usual for cooking in the toaster oven, I also had to use a larger baking pan than usual but the skewers could not reach both rims of the pan. So I had to improvise. I added another metal skewer in the back so that the chicken skewers would not sit in the juice in the bottom of the baking tray. I used the broil function of my toaster oven which turns on the upper elements to highest power. I cooked the chicken without sauce (seasoned only with salt) turning once after 8 minutes until the chicken meat was almost completely cooked. I then smeared two skewers each with one of the three sauces. I then grilled each side for one to 2 more minutes being careful not burn it. (In the picture below, from the right, tare, miso and Yuzu-koshou).
I was wondering about the name of this sake "Dassai" for some time. While I was drinking this sake, I read the label which explained the origin of this name. I supplemented this with some more Google search results. The first letter 獺 means "river otter" or "kawa-uso". The second letter 祭 means "festival". The combined word "Dassai" 獺祭 or "Otter festival" was based on the observation that after catching several fish, the otter will line them up on the river bank before eating them as though making an offering of the fish to it's ancestors. The word "Festival" obviously referred to a commemoration of ancestors such in the "obon" festival. The poet 李商隠 Li Shangyin in the late "Tang" 唐 dynasty called himself 獺祭魚 meaning "fish of the otter festival" equating himself to the fish caught by the otter as he sat among all the books and scrolls of his predecessors lined up around him to give inspiration for new poems. Later the Japanese poet 正岡子規 "Shiki Masaoka" took this name as well and called himself 獺祭書店主人 meaning "master of the otter festival book store". The sake brewery which makes "Dassai" is called "Asahi Sake brewer" 旭酒造 which is located in a small town called 獺越（おそごえ）"osogoe" in Yamaguchi prefecture 山口県. Taking one letter "otter" 獺 from the name of the place, they named their sake 獺祭 or "otter festival".