Hien (Scarlet Flame) is a magical sword that Syaoran recieved in Oto Country. Once drawn, it is able to unleash fire from its blade when used.
During the events in Oto, Syaoran realizes that his martial arts skills aren't enough to defeat Oni, thus, isn't strong enough to protect Sakura and retrieve the feathers. He approaches Kurogane to teach him how to wield a sword, and he accepts. The following day, Syaoran and Kurogane go out to buy swords for the both of them, As Kurogane's Previous sword broke in a fight with the Oni.