Pour 4 cup cold water to pot
Rehydrate kombu (dried sea kelp) in water for at least 30 minutes (preferably overnight or for several hours)
Place water and kombu in a pot and bring to a low simmer for 15 minutes
Turn off heat and add katsuobushi (dried bonito flakes)
Let it steep for 10 minutes
After 10 minutes, remove kombu and katsuobushi from water. This is the dashi stock for the soup.
Using dashi, turn on heat and add in soy sauce and chicken thighs
Cook chicken in soup for about 5 - 10 minutes (depending on size of chicken)