Though he usually acts like a calm and level-headed adult, Mosuke usually finds himself unable to restrain his emotions around Amidamaru, particularly exhibited when they finally met as spirits several centuries after their deaths and Mosuke punched Amidamaru right in the face for once again breaking Harusame.
Mosuke was born August 13, 1383 in Japan. In his childhood, Mosuke's parents were killed by bandits and he lived alongside Amidamaru and several other orphans. He had been taught by his father how to forge steel and metal. He made the katana called Harusame out of his father's knife.
In 1411, when Mosuke was 28 years old, he and Amidamaru presented their sword and services to a local lord, who hired them. The lord later asked Amidamaru to kill Mosuke because he did not want another sword created to rival Harusame. Amidamaru told Mosuke of their master's orders but planned to let Mosuke escape. Mosuke asked to borrow Harusame so that he could reforge it and improve it further for Amidamaru. They swore to meet again the next night; however, the lord sent men to kill Mosuke and Amidamaru.
After his death, Mosuke's spirit refused to leave Harusame's side until he could fulfill his oath and return the sword to Amidamru.
After Amidamaru revealed why he could not leave for Yoh and Manta, Yoh dragged Manta to the local museum in order to see the sword. Mosuke's spirit was sitting over the blade and had been doing so for over 500 years. There he told his and Amidamaru's backstory to Yoh and Manta and revealed that he was unable to pass on until he gave Harusame back to Amidamaru. After Yoh revealed that Amidamaru was still waiting for him, he used Hyoi-Gattai with Mosuke and brought the old Harusame to the nearest blacksmith for repairing. Later that night, after bringing Harusame to Amidamaru, Yoh revealed that Mosuke could not bring himself to see him and had already passed on.
When Amidamaru saved Umemiya Ryunosuke from being possessed by Tokageroh he was forced to break Harusame. To repay his debt, Ryu allowed Kyōyama Anna to summon Mosuke and place him inside his body, while Amidamaru was within Yoh's body. At first, both of the spirits punched each other in the face: Mosuke for the breaking of his sword and Amidamaru for the 600-year wait. But they were also happy to finally see each other and eventually, Harusame has repaired again.
In the manga series, Mosuke goes to the afterlife after meeting with Amidamaru. He is later summoned back when the Archangel Michael breaks Harusame so that he can repair it again. However, in the 2001 anime series, he appears again when spirit sealers want to seal Amidamaru and use a controlled Mosuke to possess Oyamada Manta and attack Yoh and the others. However, Manta figures how to create an Over Soul and uses his laptop in combination with Mosuke to create a large hammer. Later on, it is revealed that Mosuke has become trapped inside the laptop.
- When he was alive, Mosuke's blood type was B.
- The English dub of the 2021 anime switches between pronouncing his name as "Mo-Skay" and "Mo-Suu-Kay".
- Shaman King Manga - Chapter 2
- Shaman King Manga - Chapter 25, Pages 18-21
- Shaman King Manga - Chapter 299
- Blacksmith - A Wikipedia article about the profession of Mosuke.