How to Make It
Heat canola oil in a large Dutch oven over medium-high to 400°F.
Just before frying, bring master dashi, soy sauce, sake, and mirin to a boil in a medium saucepan over high. Reduce heat to medium; simmer 1 minute. Remove from heat.
Working in 3 batches, add eggplants to hot oil in Dutch oven; fry, stirring constantly, until golden brown, about 1 minute. (Eggplants should be soft around the outside and meet resistance toward the center when pierced with a chopstick.) Using a fine wire-mesh strainer, carefully transfer eggplants to hot dashi mixture in saucepan. Maintain oil temperature of 400°F between batches.
Let eggplants soak in dashi mixture at room temperature 30 minutes. Remove eggplants from dashi mixture and serve. (Discard remaining dashi mixture.)