Open natto package. Squeeze-in soy sauce packet. Squeeze-in hot mustard packet. Use chopsticks and give the natto a stir - until it begins to foam.
Set aside and chop-up a small amount of aged kimchi. Add it into the natto. Mix it in thoroughly.
Pour the kimchi & natto mixture over a bowl of hot rice. Garnish with a small handful of diced green onions.