This is some unusual charcoal.
I had a platter of robata-grilled items at Sushi Samba last week, and this Japanese grill uses binchotan, an expensive (around $10/kilo) and exclusive (not sure who else is using it) charcoal.
Dropping a stick of the stuff sounded like a glass mug hitting the floor and not breaking; tapping it with a fingernail, it emitted an almost ring-like tone. It’s very light-weight, even for charcoal, probably due to the fact that the carbonization process is so complete.
According to Dan Tucker, the chef at SushiSamba, “Binchotan actually burns at a lower temperature than hickory or mesquite charcoal; the heat curve on regular lump charcoal is parabolic [it goes up and down], probably because of the amount of unconsumed carbon; the heat curve on binchotan is more logarithmic, so it hits a plateau and stays there. Although the absolute heat is lower, the average working temp is higher,” and more consistent.
One thing I greatly admire about Japanese culture in general and their cuisine specifically is that the Japanese seem always on a quest for perfection. I doubt binchotan would be perfect for brisket, but for dishes like veggies and fish, where you want a more subtle smokiness, this charcoal seems to approach perfection.