Combine the sour cream, buttermilk, wasabi, chives and season with salt and pepper. Reserve.
Bring a few inches of water to a boil, salt it and cook the green beans, 2 minutes. Remove, cold shock in an ice bath, drain and dry on a kitchen towel.
Meanwhile, heat a few inches of oil over medium to medium-high heat. Combine 1 cup water, the flour, baking powder, onion, garlic and eggs in a bowl to form a batter. Dip the beans in the batter, a dozen at a time, and fry them up in batches. Cool on a cooling rack. Sprinkle with salt while hot.
Serve the fried beans with the wasabi dipper.