Bason

Bason is the ghost of an ancient Chinese wujiang who serves Ren faithfully and obeys him without question. In the English manga Bason calls Ren "Master Ren," while in the Japanese version he calls Ren "Bocchama," which means "Young Master." Later he became a valued friend of his young master Ren. His date of birth and blood type are unknown.

Bason has served the Tao family for several generations and has sworn to serve Ren by any means possible. He carries a kwan dao (a weapon similar to a halberd, but with one curved edge and one straight edge following the line of the handle). In his days as an ancient Chinese warrior, Bason rode into battle on a horse named Hei-Tao; the spirit of Hei-Tao can be integrated into another horse kept by Ren, named Bái-Feng, to perform the Perfect Re-enactment of the Vorpal Dance. Bason is capable of adding tremendous strength and speed to Ren's kwan dao, and even making it quite larger, but also uses his body in attacks such as the Golden Punch. In Giant Spirit Form, Bason appears as a gigantic robot capable of launching fireballs.

Like Ren, Bason appears very cold and cruel at the beginning of the series, however, following interaction with Yoh Asakura, Bason, like his master, begins to soften up and develop a much more pleasant disposition. He feels an overwhelming sense of duty to his master, even breaking down in tears when Ren is imprisoned by his father. While Bason and Amidamaru are very hostile and competitive at first, they soon become friendly rivals.

(Source: Wikipedia)