It's a common urban legend that it contains nicotine — it doesn't. It does contain nicotinamide (related to B vitamins).
In recent years, Black Black has become popular in Asia and Western countries. Japanophiles often become hopeless addicted to it.
In Japan, Black Black is available from vending machines.
In the 1990s, Jean Claude Van Damme did a series of commercials for Black Black.
Black Black packages have engrish slogans such as "HI-TECHNICAL * EXCELLENT TASTE AND FLAVOUR". If that isn't scary enough other packages are labeled "Black Black Hard".
Lotte, the company that manufactures Black Black is well known for its wild engrish slogans.