I recently went to a Japanese robatayaki called Shin Sin Gumi in LA and discovered a small plastic condiment jar of what looked at first like crystallized wasabi. I tried it a tiny dab of it on the end of my chopstick expecting it to possibly burn a hole through my nostrils to my brain, and holy saba, did it ever send salty, bitter shockwaves through my tastebuds! It wasn't wasabi. It is yuzu kosho, a condiment made from the zest of yuzu, an extremely tart citrus fruit, blended with chile peppers and salt.
I thought it was something that the chefs made, but I found a jar of it at a local Japanese market, and am now addicted to the distinctive, very bitterly pungent, yet delicious condiment. In such a small jar, it seems that yuzu kosho is used in small amounts, as it is fairly strong, but I can't help but scoop it out by the teaspoonful and add it to everything.