New thread. Talk about the anime and manga here!
Summery taken from TV Troupes because I find it somewhat funny.
The story revolves around Okumura Rin, who starts out as a boy who is somewhat of a delinquent and as such gets into fights. He is usually at odds with his adoptive father, Father Fujimoto Shirou. One day while Rin goes to a job interview that Fujimoto 'encouraged' (read 'encouraged' as 'threw objects at') him to check out, he starts seeing little black 'bugs' and runs into a group of kids he fought the other day. To his surprise, one of the kids is now a demon. Just as the demon is about to kill him, blue flames surround his body and burn his attacker. The demon realizes that Rin is the one he has been searching for: the son of Satan.
While Rin is in total shock and disbelief, Fujimoto Shiro comes and exorcises the demon. He then describes how demons come from a world called Gehenna and can cross into our world (Assiah) by possessing a vessel of sufficient strength. He takes Rin back to the house to give him a sword that seals his demon powers and see him off, but unfortunately, Rin thinks it's all bullcrap and accuses Shiro of throwing him out. Double unfortunately, Satan decides to come in and say hello. Rin saves himself, but Father Fujimoto dies in the process. After the funeral, he is confronted by Mephisto, a member of the True Cross Order and a friend of Shiro's, and demands to join the True Cross Order and become an Exorcist.