Drain the tofu well. Chop the onion. Combine all the meatball ingredients and mix well.
The mixture is very soft, so spoon the mixture gently into the cooking water. Keep the water at a simmer.
If you boil the water vigorously, the meatballs will fall apart, so be careful. Once you finish spooning the meat balls into the water, turn off the heat. Cook the meatballs through with the residual heat.
Cool the meatballs in the cooking liquid to keep them moist. Use the cooking liquid to make your hot pot and soup.
Ground chicken breast is a healthy option, but tends to be dry and crumbly. By adding tofu and reducing the amount of binding agent, you can make tender and fluffy meatballs. The cooking liquid is tasty, so do not waste it.
The only binding agent I use is an egg, so the meatballs just hold their shape. If you want to make the meatballs slightly denser, add 1 tablespoon of katakuriko. Adjust the amount to your taste. The mixture is very soft, so do not boil vigorously in the water, lest they fall apart. Instead, keep the cooking liquid simmering gently.