100 gm shredded kombu / kombu strips
80 gm soy sauce
45 gm rice vinegar
70 gm sake
25 gm mirin
30 gm sugar

Rinse the kombu, place it in a saucepan, and cover with hot tap water; let sit for 30 minutes to rehydrate.
Drain, reserving the liquid.
Add the remaining ingredients to the pot and cook over medium heat until the kombu is super tender, about 1 hour.
If the liquids boil off, replenish with the reserved liquid.
Cool completely, then mince.