Kai Chen

Kai Chen was a former province somewhere in Kara-Tur.

Some time before the mid–14 century DR, in the stadium of old Kai Chen province, up-and-coming warriors could challenge veteran samurai to ritual battles as a test of their prowess. If successful, they won lasting fame and accolades, and were gifted with the Kaga-To katana as a symbol of this.

Background
Invented as an offhand mention in Neverwinter Nights, it is unknown where in Kara-Tur this "old Kai Chen province" could be. The samurai and katana suggest Wa or Kozakura, while the Chinese-sounding name suggests Shou Lung or T'u Lung. A city called Kai Shan lies in a province called Kao Shan in Shou Lung, suggesting a changed or misinterpreted name. In any case, the in-game description "If memory serves correctly, these weapons date to the stadium battles of old Kai Chen province" suggest it is some time in the past and Kai Chen province may no longer exist by the 1300s DR.