Yoh is amidamarus main spirit ally who helps Yoh in his quest to become the Shaman King.
Amidamaru is a samurai whose past life was more than 500 years ago. He dies in a tragic battle for the honor of his best friend, Mosuke. Now, Amidamaru is a spirit who waits for his friend Mosuke at the Funabari Cemetery. When his grave is vandalize by Ryu, Yoh, who integrates with him, becomes one with him and defeats Ryu. Yoh helps Amidamaru and Mosuke gain closure, and Amidamaru, who does not want to go in the afterlife, becomes Yoh's spirit ally for the Shaman King Tournament.
Amidamaru and Mosuke lives as orphans during the warring period of feudal Japan. Mosuke helps Amidamaru by forging swords, but Amidamaru breaks them because Amidamaru helps protect the orphans and themselves from
samurai and enemies. Later, Mosuke forges a sword that is made from his prized father's knife. Years later, Amidamaru and Mosuke travel to present Harusame to the feudal lord. The sword impresses the lord that he accepts Amidamaru and Mosuke as his vassals. However, the feudal lord wants the sword to have a scarcity value, and he instructs Amidamaru to kill his best friend because the sword Harusame must not have any sword greater than it. Later that night, Amidamaru tries to persuade Mosuke to leave, but Mosuke wants Amidamaru to lend Harusame to him so Mosuke can forge it better than the lord's sword. Yet, the feudal lord's men murdered Mosuke and Amidamaru without his best sword fights the lord's men. This is why Amidamaru becomes the fiend as he
slaughters most of the lord's men before dying to exhaustion. Most importantly, Amidamaru learn that he must sacrifice anything to save a friend during the Tokagero fight.
Tokagero is a warrior that Amidamaru killed 500 years. Amidamaru sees Tokagero who is looking for revenge by possessing Ryu and threatens to kill Ryu or Manta or break his sword. After Yoh integrates with Tokagero, Tokagero, who thought that he has revenge, cries because he does not have the heart to kill Yoh due to his compassion and generosity. Tokagero leaves Amidamaru and his friends with a lesson learn. After the Shaman King preliminaries, Amidamaru meets Tokagero who is Ryu's partner, and the two are good friends. Their friendship is observe in volume 9 when they share a conversation before Yoh and Anna's implied sex scene.
Amidamaru is created by Hiroyuki Takei, and he has no information regarding any inspiration used by the author to create him. He first appears in Shaman King volume 1 and episode 1. His Japanese voice actor is Katsuyuki Konishi while for the child version, his Japanese actress is Mitsuki Saiga. His English voice actor is Sean Schemmel.
Amidamaru does not change much, but only during the Tokagero incident, he learns that saving the life of a friend matters more than saving a friend's treasured item.
NOTE: These are not official arc names due to the lack of information from the author and notes in the manga.
NOTE: The information below is manga only info. See anime differences under "anime and manga differences" paragraph.
After Bokuto no Ryu vandalizes Amidamaru's grave, Yoh Asakura lends a hand to Amidamaru by integrating with Amidamaru. Yoh uses Amidamaru's expert swordmanship and kick out Ryu and his gang out of the cemetery. This marks the beginning of Amidamaru's friendship with Manta and partnership with Yoh before the Shaman King fights. When Yoh and Amidamaru first meet Ren Tao, the two young shamans fight. Although Ren has the upper hand on Yoh due to Ren's 100% integration, Yoh and Amidamaru finally integrate 100% near the end of the battle. Somehow, Yoh and Amidamaru defeat Ren and the two shamans collapse. As soon as Yoh wakes up, Manta and Amidamaru, who are at the hospital, greets Yoh and tell him what happen. Amidamaru blames himself for not protecting Yoh, and Anna barges in. Soon enough, Amidamaru, who is surprised, finds out Anna is Yoh's fiancee. After Anna informs Yoh, Manta, and Amidamaru about the upcoming Shaman King tournament, Yoh and Amidamaru train rigorously under Anna's regimen because Yoh is a lazy fool.
Amidamaru's first shaman test with Yoh appears after planet Rago (a meteor) appears and signals the start of the tournament. When Yoh and Amidamaru meet Silva, he appears to be a normal salesman who sells Native American Crafts. Amidamaru's real test comes when Silva fights Yoh and him. After Yoh integrates Amidamaru into Harusame, Yoh uses his new oversoul (Amidamaru) and lands one hit on Silva. Amidamaru rushes to Yoh's side when Yoh collapse from mana exhaustion. Yoh and Amidamaru are officially in the tournament.
During the first preliminary match with Horohoro, Yoh and Amidamaru defeats Horohoro's greatest avalanche move. When Yoh's second preliminary match with Faust comes, Yoh suffers his defeat when he wastes his manta in anger after attempting to save Manta, whose ribs are open by Faust. After Yoh collapses from fatique, the angry Faust tries to attack Yoh, and Amidamaru tries to stop him. However, Ren appears and destroy's Faust's giant oversoul skeleton. After Yoh's first defeat, Amidamaru, Yoh, and Anna head to Izumo where Amidamaru waits patiently for Yoh's return from his training in the cave of Yomi. The result of Yoh's new training is Yoh's new oversoul and Amidarmaru can talk in this form.
Yoh's last preliminary match with Ren is the toughest battle yet. Yoh's oversoul is smaller than Ren and packs less mana, and Ren has more mana than Yoh which makes the battle difficult for Amidamaru and Yoh. The advantage of Amidamaru's new oversoul is that Amidamaru can tell Yoh when to dodge and he can strike at will. The battle's result is a tie when the two shamans' oversoul fades away at the same time.
Amidamaru accompanies Yoh and the other shamans to China when Bason, Ren's ghost, asks Yoh and friends to help Ren who is held captive by his father, Tao Yuan. In the end, Ren defeats his father because Ren's father's will waver. When one's will is wavered, one's oversoul gets weaker.
Amidamaru witness the great desert of America and he meets Lyserg, Hao's followers, X-Laws, and many more. After Yoh and his friends sees Hao Asakura and his followers for the first time, they climb aboard the Patch jumbo airline to America. Suddenly, the Patch reveals their true intentions when they tell the shamans to reach the Patch Tribe in three months or be disqualified. As the Patch Tribe cancel out their oversoul, the plane shatters (it's an oversoul) leaving the shamans to figure out to land safely.
The encounter of Lyserg and Hao's followers is a dangerous one. When Yoh's friends are injured by Lyserg who tries to prove his abilities, Yoh tells Lyserg he will never let him join because he hurt his friend. When Lyserg lashes out, Yoh uses Amidamaru to destroy Lyserg's spirit medium. Yet, Lyserg does not give up and attacks with another pendulum, and Lyserg uses his best technique, Big Ben. Yoh and Amidamaru counters with Amida-Style Halo Blade. After Yoh lets Lyserg join them, the next battle that Amidamaru fights with Yoh and gang is with Hao's followers. In front of the cave that leads to the Patch Tribe (at Mesa Verdede), Hao's followers, Mohamed, Boris, Zang, Big Guy Bill, and Damayji, are blocking the entrance. Mohamed tells Yoh and gang that they will kill Yoh's friends due to Hao's orders to test Yoh. Near the end of the battle, Boris has Yoh's team in a tight situation. Specifically, Lyserg, who is controlled by Blamuro, points Harusame to his neck while holding Yoh. Ryu, Ren, and Horohoro have bloody stakes in the air ready to impale them. Yet, Yoh, who is very calm, tells Boris that he will do what is necessary, and Amidamaru, who talks to Blamuro when Boris's stakes are destroy, rekindles Blamuro's conscious which causes Blamuro to stop obeying Boris. After Ryu defeats Boris, Amidamaru sees an Arch Angel killing Boris when Yoh tries to help Boris. This is the first time that Yoh and gang sees the X-Laws. In the cave, the X-Laws de facto leader, Marco, tries to kill Big Guy Bill, but Yoh steps in to intervene. After Marco and Yoh clash, Yoh's harusame breaks into two which Amidamaru looks at it in despair. Amidamaru and Yoh train with Faust and Ryu under Anna's regimen in Patch Village.
After a time skip of two months, Yoh and Amidamaru with the rest of the shamans head back to Tokyo. Amidamaru and Yoh's team is Funabari Hot Spring and their team mates are Ryu and Faust the VIII. Their first battle is with the Ice Men. (see volume 15) After mastering the Ultra Senji Ryakketsu, Yoh can integrate Amidamaru with Harusame and integrate that to Futsu-no-Mitama no Tsurugi. This "compound oversoul" creates an enormous sword that has a long length. Yoh and Amidamaru defeat Ice Men team with one slash after the leader and his team mates agreed to use all of their furyoku in one last final attack against Yoh.
In the manga, Amidamaru's origin story is more bloody due to how graphic the scenes are compared to the anime. The anime version only reveal a tiny bit of Amidamaru's rise to fiend scenes.
Just like all Shaman King characters in the anime, Amidamaru meets characters earlier than the manga counterpart. These people are Horohoro and his spirit ally and more.
Amidamaru's techniques are alter from manga to anime because some abilities are manga exclusive while others are anime exclusive. For example, ___.
Amidamaru is the spirit ally of Yoh, so it is really Yoh's techniques since Yoh integrates Amidamaru into various swords and manipulates his furyoko to develop different attacks.
Yoh can integrate with Amidamaru 100% and uses two techniques. Amidamaru has a flame ball form seen in both manga and anime.