Author Hiroyuki Takei chose shamanism as the series' central theme specifically because it was a subject that had never been explored in manga before.

Before creating Shaman King, Takei worked as an assistant on Nobuhiro Watsuki's Rurouni Kenshin and exchanged ideas with fellow assistants, including One Piece creator Eiichiro Oda.

Takei was influenced by street art from hip-hop and rap culture, which is visible in his manga artwork, and he used calligraphy inks, pen nibs, and Copic brand markers for his illustrations.

Takei said he created characters first and stories second, believing that 'stories are born because of the existence of the characters.'

The manga ended abruptly in 2004 after being cancelled due to low reader poll rankings in Weekly Shōnen Jump; the final tankōbon volume's last scene shows a mikan (mandarin orange), which Takei intended as a joke signifying the story's incompleteness.

Takei stated the cancellation was not due to declining profitability but to his own creative 'fatigue,' as he felt the series was being 'normalized' by fan expectations and losing its originality.

After the abrupt ending, a handwritten letter from Takei was read on the radio show 'Megumi Hayashibara's Tokyo Boogie Night,' revealing that he had not wanted the series to end that way.

In 2007-2008 the series was fully reprinted as a 27-volume 'kanzenban' (Perfect Edition) that finally gave the story its true, intended ending, adding about 380 new pages that had never been published before.

For the 2021 anime remake, the role of protagonist Yoh Asakura was recast to Yuko Sato's successor Yoko Hikasa (Yōko Hikasa/Hikasa Yoko), chosen through an audition; producer Akiko Yada praised her for capturing the character's relaxed yet resilient core.

Director Seiji Mizushima revealed in 2020 that the original, non-manga storylines added in the second half of the 2001 anime were not his own idea but were requested by original publisher Shueisha.

Takei was offered a chance to make a second anime adaptation earlier but turned it down after being told the new series could not use the original voice actors or soundtrack music, hoping instead for a future opportunity that later became the 2021 remake.

The 2021 anime series is based on the Kodansha 'KC complete edition' of the manga and was the first adaptation to animate the story all the way through to its true completed ending, including the previously unanimated 'Osorezan Le Voyage' arc.

In 2004, the Aomori Prefectural Police's Mutsu station chose the character Anna Kyoyama as the mascot for its newly launched website.

Shaman King has sold over 38 million copies in circulation in Japan as of March 2021.