Combine chicken with miso, ginger, mirin, and 4 tablespoons of vinegar in a bowl.
Cover and refrigerate the chicken to marinate for at least 3 hours or overnight.
Boil shallots in water for 5 minutes, then strain and halve them lengthways.
Grill chicken skin-side up on a baking tray with marinade for 10 minutes on high.
Sauté shallots in sunflower oil for 4 minutes until browned.
Add remaining vinegar, wine, water, salt, and pepper to the pan and cook for 6 minutes.
Transfer grilled chicken and juices to the pan and simmer covered for 4 minutes.
Remove chicken and stir walnuts, butter, maple syrup, and grapes into the sauce for 3 minutes.
Spoon the emulsified sauce over the chicken and garnish with chopped tarragon.