Yamaroku Soy Sauce's overwhelmingly popular product is called Tsurubishio. It takes 4 years to be brewed, which is unprecedented even in Japan.
Normally, Koikuchi (regular color) soy sauce is brewed with salted water. However, as Tsurubishio is a Saishikomi soy sauce, it is double-brewed by using soy sauce instead of salted water.
After 2 years of aging, this soy sauce is brewed in the barrel for 2 more years. It is a soy sauce that pursues a richness and softness of taste. It goes well with vanilla ice cream, sashimi and meat along with wasabi and soy sauce.
The best way to enjoy this product is to just pour it over your food.