Legend of the Millennium Dragon (aka Onigamiden) starts off with a battle between samurai and Oni, "visualized demons that seem to be made of smoke". It does not go well for the samurai and as the Oni prepare to make their final push to destroy a local temple, but Monk Gen'un wipes them all out in one blow with his magic powers.
The film then shifts focus over to Jun Tendo, a shy teenage boy, who is transported 1200 years into Japan's past to the Heian era. There, he must enlist the aid of the dragon Yamata no Orochi to resolve a war between humans and Oni.
He is bullied over and over because of his weak appearance and lack of skills.
Jun is then followed and attacked by an Oni, which he runs away from. While running, Jun finds himself hiding in the temple of Monk Gen'un and is confronted with the truth. Monk Gen'un starts by telling Jun that he is being targeted by the dark monsters and about the war between humans and Oni back in the Heian era.
Jun passes out and wakes up at the temple where he meets Raiko Minamoto, a highly skilled swordsman that fights alongside of Gen'un. Jun is treated as royalty and is highly confused.
