Wipe the chicken thigh fillets dry with paper towels then cut into cubes. We like 2"x2" cubes but you can make them slightly larger or smaller than that.
Place the chicken cubes in a bowl, add the soy sauce, mirin and ginger, and mix well. Cover the bowl and marinate in the fridge for 30 minutes.
In a fryer, heat enough cooking oil to reach a depth of at least three inches.
Drain the chicken and dredge each piece in starch.
Over medium heat, fry the chicken cubes in batches. Three to four minutes per batch or just until the coating starts to turn crisp. The chicken will look pale at this point but don't worry. As each batch finishes cooking, transfer to a rack.
When all the chicken cubes have been fried, turn up the heat to high.
Fry the chicken cubes a second time, in batches, for another two minutes.
Scoop cooked Japanese rice in bowls, pile shredded cabbage and kalamansi halves (or lemon wedges) on one side and arrange several pieces of chicken karaage on top.
Squeeze kalamansi (or lemon) juice over the chicken before eating.