De-bone your chicken thighs and cut into 1 inch, bite-sized pieces.
In a bowl, add soy sauce, sake, ginger, garlic, and mirin together and stir until all ingredients are combined.
Add the 1-inch chicken pieces to a container with a lid (I like to use glass food storage containers with a rubber seal for marinating because it seals liquids properly).
Mix in the marinade and stir to cover all the pieces of chicken. Close the lid and leave in the refrigerator for at least 6 hours. You will want to check at the 4 hour mark and give it a mix to ensure even coverage.
After your chicken is done marinating, pour about 1 ½ inches of vegetable oil in a heavy bottomed pot and heat to 375 °F degrees.
Measure out 200 grams of potato starch into a shallow bowl. Lightly flour each piece of chicken into the potato starch. Add more starch to the bowl if necessary. If you can’t find potato starch, you can also substitute it for cornstarch.
Immediately after breading, you want to slowly lower each chicken piece into the heated oil. Make sure to not crowd the pieces to ensure proper frying.
Cook each piece for about 3-5 minutes depending on the size, or until golden brown.
Remove the chicken and place on a cooling rack or paper towels to remove excess oil.
Serve the karaage with lemons and Japanese mayonnaise (Kewpie brand) topped with Shichimi Togarashi, if you want an extra kick. Enjoy!