Lord Sesshoumaru is Inu Yasha's half-brother. They shared the same father. Sesshoumaru's mother was also a demon, unlike Inu Yasha, and therefore is full demon. Sesshoumaru dislikes his little brother greatly and shuns him for his human tinged blood. Sesshoumaru sometimes fights with a poison whip. Later on his main weapon is the Tokijin sword. Sesshoumaru also possesses the Tensaiga, but he uses it very rarley, as it does not have the power to kill, as the Tetsusaiga does.
Tokijin, was forged by the fang of a demon with one purpose-to kill Inu Yasha. Over time, Sesshoumaru finds great power within this sword, and is his main weapon in battle. The Tenseiga, given to him by his father, has the power not to kill, but to grant life. He uses this sword to save his companion, Rin, who travels with Sesshoumaru all the time. Sesshoumaru also has a hidden weapon-the poison whip, attached to his nail, which could kill any human with a single touch.
Sesshoumaru, being a full demon, still shows key traits, such as honor, and decency. He never does try to kill Inu Yasha, though he says he wants him dead, but always fights to the best of his potential. He, unlike other demons, will never kill humans without a sole purpose, or if they were to harm his companions. Sesshoumaru also lightens up to the race of humans over time, and rethinks their ability in life.