Amidamaru

Samurai that died during the Muromachi period 600 years ago - now is Yoh's ghost companion. He is very powerful and wise but quite taciturn and extremely devoted to "Lord Yoh" ("Yō-dono" in Japanese). He was greatly known around the town of Funbari, where he had died 600 years prior after killing several hundred other samurai soldiers during a battle. He is the original handler of the legendary sword named "Harusame", meaning "Spring Rain", a sword forged by his best friend, Mosuke, who also appeared in the anime/manga as a spirit. This very same sword was reproduced as a "spirit sword" and used by Asakura Yoh during the Shaman Fight. The original was kept in a museum. His name is based on the Buddha Amitabha, the principal figure in the Pure Land Buddhist sect.

(Source: Wikipedia)