Overview
Amidamaru is introduced in Reincarnation 01 in Shaman King as the ghost of the grave destroyed by Wooden Sword Ryu, a local delinquent leader who claimed the area around Funbari Hill's cemetery as his own private area. The samurai is rumoured to have been an infamous fiend who killed many people before he died, though little else is known about him. When Manta Oyamada and Yoh Asakura, two local high school students, begin frequenting Funbari Hill's cemetery, Manta is beaten up by Ryu. Yoh decides to avenge his new friend and reveals his power as a shaman and asks for Amidamaru's help to take down Ryu and his gang. Amidamaru agrees and Yoh uses the Spirit Integration technique in order to utilize Amidamaru's fighting abilities to defeat Ryu.
When Yoh asks Amidamaru to become his spirit ally, the samurai ghost initially refuses for personal reasons. Manta discovers that Amidamaru has been waiting on Funbari Hill for six-hundred years and after a trip to the local museum, he and Yoh learn that Amidamaru has been waiting for his friend Mosuke to deliver a sword to the hill. After Yoh delivers Mosuke's sword to Amidamaru at last, the samurai agrees to become Yoh's guardian ghost and faithfully stays by Yoh's side. Mosuke's sword, Harusame, later becomes the primary medium that Yoh uses for Amidamaru's spirit in combat. After meeting Yoh, Amidamaru becomes acquainted with many of Yoh's friends and forms friendly relationships with the spirit allies of other shaman, particularly Tokageroh, a bandit from the Muromachi era who initially holds a grudge against Amidamaru, and Bason, the ghost of a powerful Chinese warlord.
As Yoh's guardian ghost, Amidamaru proves to be a trustworthy and powerful spirit ally. As a samurai, he is highly experienced in combat and specializes in fighting one-on-one with opponents who are considerably stronger than he is, possessing remarkable visual acuity. In addition, his six-hundred-year existence as a ghost allows him to change his form according to Yoh's will and regain his original form when he is not in combat. While he is taciturn and dedicated to Yoh, Amidamaru expresses anxiety towards being unable to become stronger in order to aid his master because he is a ghost. Nevertheless, as Yoh becomes increasingly powerful as a shaman, he becomes able to draw out more of Amidamaru's strengths and the two prove to be challenging opponents to defeat. At the conclusion of the series, he becomes the guardian ghost of Yoh and Anna Kyoyama's son, Hana Asakura.
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