The practice of onmyoudo was inspired and influenced by Chinese occultism: ie. feng shui and Taoism and became one of Japan’s most influential art forms around the 5th century. The practitioners, Onmyouji, held tremendous sway in imperial courts and on noble lords. They were foretune-tellers with the ability to exorcise evil and vengeful spirits. Whole families dedicated themselves to the art, and one such family was the Abe family. Abe no Seimei held great prominence in Japanese history during the Heian period and is a legendary figure in Japanese folklore.
Shonen Onmyouji 少年陰陽師 tells the story and journey of Abe no Masahiro, the grandson of the great omnyouji Abe no Seimei.
Abe no Seimei has 12 shikigamis under his command, which protect him and his family. He is also able to project his soul, as his younger self, to aid his grandson in times of trouble.
Masahiro lost his ability to see spirits as a child when his grandfather sealed it for his own protection. Down the road, he stumbles upon a mononoke that he names Mokkun, a fox-like creature that only a few can see, who shows him his true potential as the heir of the Abe family. Mokkun is one of the 12 shikigami under Seimei’s command who specifically chose to follow and protect Masahiro. Mokkun is ostracized by the rest of the shikigami because of his previous actions against his master, although Seimei doesn’t blame him for that misunderstanding. Together with Mokkun (who he calls Guren) as his guide, Masahiro strives to become his grandfather’s true and only successor. Through his nightly protection of the city, he gains strength and hones his craft. He is finally sent to protect Princess Akiko of the Fujiwara clan, who he falls in love with.