Legend of the Millennium Dragon

Legend of the Millennium Dragon , Onigamiden? is a 2011 Japanese anime film.

During the night the temple is attacked by Oni. The humans retaliate and fight back to protect their temple and their savior Jun. Jun is a descendant of the Magatama clan with a birthmark on his left shoulders. Only direct bloodlines with that birthmark can awaken the full powers of a mystical dragon Orochi. In order to summon the dragon to save Raiko and everyone else in the village, Jun must chant the incantation. Jun sees that Raiko is in deep trouble and screams his name while awaking the powerful dragon in the process without the incantation. Jun awakes finding himself riding on the back of Orochi, which becomes Juns servant and source of power.Jun comes in conflict with Mizuha, an Oni, and find out that they are not the demons that everyone makes them out to be. Instead of being demons, the Oni are regular people that wears a mask which causes the visualization of the demons. Jun shortly finds out a different story than what Genun has told him from the Oni and now wants answers. He feels both side of the stories and does not know who to trust. Mizuha singles out Jun and asked him to join them and fight to project their cause, but Jun refuses to make such a quick decision because he wants to trust both side. Jun gets pressured by the Mizuha and calls upon Orochi to escape. Mizuha jumps on Orochi and escapes with Jun, but they soon hit an Onifree barrier and gets struck down by magic power. Jun wakes up to find himself with Tsuna and Kinta, Raikos fellow swordsmans, whom has been searching for Jun to meet up with Raiko. ........

Source: Wikipedia