In a medium saucepan over very low heat, gently warm the soy milk with the piece of kombu, then take it off the heat and leave to infuse for about 30 minutes.
Return the pan to the heat and add the miso, yuzu paste, and soy sauce. Cut the block of tofu into quarters, then cut each quarter in half crosswise. Add the slices to the soup and poach them over low heat for 5 to 10 minutes. Fin