A chronology of konbu production in Japan, “Konbu ko”, the word konbu shows up in Chinese documents as early as the third century. It is likely derived from kompu, an Ainu word referring to things that grow on underwater rocks.

As Japan is a volcanic country with largely acidic soil, and konbu is an important alkaline food that neutralizes our bodies as well. It also plays a role in purifying the ocean. When we hear about oil tankers sinking, konbu purifies the oil-contaminated water in about seven years. Konbu greatly contributes to reducing carbon dioxide.

In earliest times konbu was eaten as a source of salt by stewing until it lost shape. The custom of making stock with konbu is thought to have originated around the tenth century. But now, after a millennium, this ancient tradition is beginning to erode from underneath.

Hosome-konbu period (L. religiosa)
Era circa 1220
Productive center is from Matsumae to Hakodate Pruduction

It seems that shio-konbu boiled with soy sauce was cooked using L. religiosa in the Sengoku period (period of warring states), which was served in the ceremony to go into a battle as lucky foods along with dried chestnuts, because the sound of konbu (kelp) made people think of joy, joy is “yoro-kobu” in Japanese, “yoro-kobu” and “yoro-konbu” have similar sounds, and dried chestnuts made them think of victory, dried chestnuts are called “kachi-guri”, literally, victory and chestnut in Japanese.

http://www.tokyofoundation.org/en/topics/japanese-traditional-foods/vol.-21-konbu-kelp