• Gather all the ingredients.
  

To Wash the Rice

• Quick Rinse: Add just enough tap water to the bowl to submerge 1½ cups uncooked Japanese short-grain white rice. Then, discard the water immediately. Tip: Rice absorbs water very quickly when you start rinsing, so this quick rinse helps remove impurities from the rice and prevent it from absorbing the first few rounds of milky water.
  
• Wash: Next, use your fingers to gently agitate the wet rice grains in a circular motion for 10–15 seconds. Don‘t use a strainer as it can break the rice. Tip: Using very little water allows the grains to rub against each other. It also reduces the absorption of impurities from the milky water.
  
• Rinse: Add tap water and immediately discard the cloudy water. Repeat one more time.
  
• Repeat the Wash and Rinse process (steps 2 and 3) one to two more times.
  
• Drain: When the water is almost clear, use a fine-mesh sieve to drain and shake off any excess water. Do not leave it for more than 5 minutes as it can easily get too dry.
  

To Prepare the Ingredients

• Mince ½ onion finely (called mijingiri in Japanese). Lay it flat side down on the cutting board. With the knife edge toward the root end, make ⅛-inch horizontal slices to within ½ inch of the root end, keeping the root end intact. With the knife tip pointing toward the root end, make ⅛-inch vertical slices, again keeping the root intact.
  
• Make perpendicular cuts down through the vertical slices you made. To chop the onions finer, run your knife through them using a rocking motion. Hold down the tip of the knife; otherwise, the onions will go flying around the room.
  
• Next, trim the fat from 6 oz boneless, skinless chicken thigh. Then, angle your knife back and diagonally (so it‘s nearly parallel to the cutting board) and cut the chicken against the grain into thin strips. This Japanese cutting technique is called sogigiri.
  
• Cut the chicken strips into ½-inch (1.5-cm) pieces, again using the sogigiri technique.
  

To Cook the Ketchup Rice

• Add the well-drained rice to the inner pot of the rice cooker. Then, add ⅓ cup ketchup and 2 tsp Worcestershire sauce.
  
• Add 1¼ cups water. Mix it all together with a spatula.
  
• Add 1 tsp Diamond Crystal kosher salt and freshly ground black pepper. Mix again, then level the rice.
  
• Scatter the minced onion on top of the rice in a single layer. DO NOT MIX.
  
• Add the chicken pieces on top in a single layer. Do not mix.
  
• Add 1 bay leaf (dried) and 1½ Tbsp butter on top. Close the lid, select the Regular cooking mode, then press the Start button. If your rice cooker does not have soaking time added into the cooking program, let the rice soak in the liquid for 10–15 minutes before you press Start.
  
• Once the rice is done, add 2 Tbsp green peas (cooked).
  
• Remove the bay leaf. Then, gently fluff with a rice paddle to mix in the ingredients and serve.
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days or in the freezer for a month. Japanese people always freeze leftover rice to keep it from getting hard in the refrigerator. Reheat the ketchup rice in the microwave until warm.