Season the chicken lightly with salt and black pepper. Place it skin-side down in a pan and cook until the skin is golden brown. Flip the chicken and cover to steam-cook until done.

In a small bowl, mix together the sake, mirin, and shoyu koji. Once the chicken is cooked through, turn off the heat and add the sauce mixture, tossing to coat the chicken evenly.

If making shoyu koji paste is too much trouble, you can add it as-is and simmer the sauce a little to thicken. Be careful not to over-reduce, as it can burn easily.