Humans and demons are two sides of the same coin, as are Assiah and Gehenna, their respective worlds. The only way to travel between the realms is by the means of possession, like in ghost stories. However, Satan, the ruler of Gehenna, cannot find a suitable host to possess and therefore, remains imprisoned in his world. In a desperate attempt to conquer Assiah, he sends his son instead, intending for him to eventually grow into a vessel capable of possession by the demon king.
Ao no Exorcist follows Rin Okumura who appears to be an ordinary, somewhat troublesome teenager—that is until one day he is ambushed by demons. His world turns upside down when he discovers that he is in fact the very son of Satan and that his demon father wishes for him to return so they can conquer Assiah together. Not wanting to join the king of Gehenna, Rin decides to begin training to become an exorcist so that he can fight to defend Assiah alongside his brother Yukio. [Written by MAL Rewrite]
A brave young warrior named Guts fights for his fortune as a mercenary on the front lines. A fated encounter unites Guts with the charismatic and deadly young man named Griffith. Leading the rogue soldiers known as the Band of the Hawk, Griffith wields his formidable force like no other. Driven by a quest for status, the Hawks exert military and social prowess the likes of which have never been seen before. The armies of Midland will quake with fear as Griffith and Guts set off on a path that will bring the world to its knees. (Source: Season One Complete DVD Collection Back Cover)
“Will you kill someone you love because of love?” The Japanese Ministry of Defense has an anti-paranormal special forces group called the Supernatural Disaster Prevention Office. They are the ones responsible to protect Japanese soil and its people from supernatural and paranormal events. However, things didn’t go so well in one of their missions… (Source: ANN)
The story follows the “strongest juvenile delinquent,” Tatsumi Oga, a first year at Ishiyama High, the school for delinquents. One day while sleeping next to a river, he sees a man floating down it. Tatsumi pulls him to shore, and the man splits in half revealing a baby boy. This boy is the son of the demon king, and Tatsumi has been chosen as the one to raise it with the baby’s demon maid, Hilda. The story follows his life with the child at the delinquent school. (Source: Wikipedia, edited)
In feudal Japan, evil spirits known as mononoke plague both households and the countryside, leaving a trail of fear in their wake. One mysterious person has the power to slay the mononoke where they stand; he is known only as the Medicine Seller, and he vanquishes the spirits using the power of his Exorcism Sword. However, in order to draw his sword he must first understand the Form, Truth and Reason of the mononoke. Armed with a sharp wit and keen intellect, the Medicine Seller wanders from place to place, striking down the evil spirits in his wake. (Source: Flatiron Film Company)
References: Wiki, MyAnimeList,