Nigari Tofu is tofu that has been made from soy milk curdled with brine (Nigari.)
The brine is actually magnesium chloride, a byproduct of extracting salt from seawater.
Most other tofu made now uses Calcium sulfate because it is less demanding.
But Nigari tofu is much healthier and with a slightly natural taste!
It's also specialty tofu in Taiwan.