Jashin

Jashin (ジャシン, wicked heart; evil design) is the god that the Akatsuki member Hidan worships. Jashin, according to Hidan, expects that all followers of Jashin - so named "Jashinists" - bring nothing less but utter destruction and death. Always before a fight, Hidan prays to Jashin, asking for a 'good kill.' If he is unsuccessful, or is not allowed to kill, he prays for forgiveness.

When undergoing a sacrifice, Hidan changes appearance. His skin turns black with white markings representing a skeleton, a symbol of absolute death. He draws Jashin's symbol in the ground in blood and stands in the center.

This symbol is an equilateral circumscribed triangle (a triangle with a circle around it). Once his sacrificial ritual takes place, the victim can be considered dead unless Hidan either steps or is forced out of the circle. Any kind of pain that Hidan inflicts upon himself is inflicted upon his sacrifice, be it a mere scratch or a pierce in the heart. This is called "Sorcery: Death Controller Possessing Blood"

Hidan is the "successful experiment of the Jashin religion's secret jutsu", which allows him to become immortal, whether it is fatal wounds or dismemberment (though he needs his head to be attached to his body in order to move). He uses this to advantage to otherwise fatally injure himself while he is linked to his opponent in order to kill them. If he goes without killing people for a certain amount of time, he loses his immortality.

A sin in Jashin's eyes would be anything that is not corruption or carnage. Jashinists practice the act of chastity, meaning they do not engage in the acts of sex (presumably). Mammon, or greed, is a sin as well (not proven).