Place seaweed into a bowl and cover with water. Soak until soft, 5 to 10 minutes. Drain and cut into 2-inch pieces.

Heat sesame oil in a saucepan over medium heat. Add beef, 1/2 tablespoon soy sauce, and salt; cook and stir for 1 minute. Stir in drained seaweed and remaining 1 tablespoon soy sauce; cook, stirring frequently, for 1 minute.

Pour in 2 cups water and bring to a boil. Stir in garlic and remaining 4 cups water. Bring to a boil again, then cover and reduce the heat. Simmer for 20 minutes. Season with salt before serving.