Add 100 ml dashi stock, 1 tbsp Japanese soy sauce (koikuchi shoyu), 1 tbsp mirin, ¼ tsp sugar, and 1 dried red chili pepper to a small saucepan. Place on the stove over medium heat and bring it to a boil. Boil for 1 minute, then remove it from the heat and leave to cool.
Wash 2 eggplants and cut off the stems. Cut in half lengthways and make shallow, diagonal slices across the skin side. (Each incision should be about ½ cm apart.)
If you have small eggplants, cut them in half horizontally. If you have longer eggplants, cut them into thirds or quarters.
Heat your oil to 170 °C (338 °F) and add the eggplant with the skin side facing down, fry for 1 min on each side. Fry 6 shishito peppers for 1 minute.
Remove the eggplant and shishito peppers from the oil and place them in colander sitting over a large heat proof bowl. Pour boiling water over the to wash off the excess oil. Make sure they are not sitting in the hot water.
Place the eggplant and shishito peppers in the agebitashi broth and rest on the counter top. Once cool, cover and chill in the refrigerator for at least 30 minutes.
Divide between serving bowls and serve with 1 tbsp grated daikon radish (daikon oroshi) and finely chopped green onions. Enjoy!
Notes
Keep half the oil surface showing: The more pieces go in at once, the further the oil temperature falls. When the fine bubbles settle, the heat has dropped. Wait for them to come back before the next batch goes in.Only pour the hot water over: Leave the eggplant sitting in it and the umami and the purple pigment wash out along with the oil. The oil held inside the flesh stays put, and it floods out with the dashi in every bite.Sink them into the broth while they are hot: Eggplant added after it cools only takes flavor on the surface. Scored and still hot, it draws the broth all the way in as it cools.Do not stack the fried eggplant: Spread it in 1 layer in the colander. Stacked pieces steam, and the skin changes color wherever they touch. For a big batch, use 2 colanders or move pieces into the broth in the order they got hot water.The oil film is what holds the purple: Fry the eggplant skin side down as soon as it is cut. Time in water sends purple into the broth, and cut faces left waiting turn brown.If it comes out heavy and greasy: Lift the eggplant out of the broth, spread it in a colander and pour just-boiled water over it again. Chilled, the floating oil sets white on the broth, so skim it off before the eggplant goes back in.