Charcoal made from hardwood is called Binchotan, they take this hardwood and pyrolyze it (use intense heat to convert most of the wood into carbon) like other charcoal.
The process used in Japan has been refined and improved to get a much higher carbon content than western lump charcoal by and heating it at the normal 400-700℃ range for awhile, and then quickly raising the temperature to over 1000℃, then quickly cooled using a white powder of earth, sand, and ash.
Binchotan is sometimes called ‘white charcoal’ after the white dust that is sometimes left on it from the smothering process.
This process results in making it almost pure carbon. While binchotan is typically thought to burn hotter than other charcoals, this isn’t necessarily true.
The truth is it burns cleaner, longer and at a more consistent temperature.
It lasts for anywhere between 3-6 hours and usually keeps a temperature of around 370℃ (700℉).