Hidan

Hidan and Kakuzu were in charge of capturing the two-tailed cat bijuu Jinchuuriki. This kunoichi named Nii Yugito from Hidden Cloud was highly skilled and not easily captured by the pair. Hidan managed to defeat her and nailed her to a wall in preparation for his rituals. After the battle Zetsu took their prize and the duo traveled to the Fire Country. Their target was a Jinchuuriki but Kakuzu had them take a side journey to capture a bounty. The two men invaded the Fire Country temple, killing many of its monks including Chiriku, a former Twelve Guardian.

With their bounty in hand they traveled to a nearby bounty station. Unfortunately one of the monks survived and fled to Konoha to bring word of the massacre. Squads were dispatched and a team of Asuma, Shikamaru, Izumo and Kotetsu tracked the duo down. Asuma and Hidan began to do battle and Hidan told his partner to stay out of the fight.

Hidan managed to dodge and avoid most of Asuma strikes, all the while starting his Jashin ritual. With the ritual begun, his body turned dark and a skeletal outline appeared on his skin. Using some of Asuma's blood he managed to connect his pain and damage back to Asuma. When Asuma unleashed a fire element attack upon Hidan, the damage was also felt back on himself. As Hidan reveled in the pain the Konoha ninja began to freak at the strange foe before them. Shikamaru managed to catch Hidan with his shadow and withdraw him from his ritualistic symbol. This gave Asuma the opening to hurt Hidan without it damaging him as well. Charging with his Flying Swallow technique, he cut off Hidan's head, sending it flying.

To Konoha's surprise the head cursed at them and Kakuzu finally stepped in after Hidan relented to needing help. Showing his immortality, Hidan's head was sewn back on by Kakuzu. The insane man then stepped back into the Jashin symbol and stabbed himself through his chest, critically wounding Asuma in turn. When Izumo and Kotetsu tried to assist, Kakuzu stepped in and showed he was no slouch. Things looked grim until reinforcements from Konoha arrived. Asuma was removed to safety and the Akatsuki members were forced to back peddle. They were set on finishing the fight but their leader contacted them, requiring them to return and assist in sealing the recently captured Sanbi demon in the King of Hell statue.

After sealing both the Nibi and the Sanbi, Hidan and Kakuzu moved to find their second Jinchuuriki. On their journey they were stopped by Team 10 and Kakashi. Team 10 was set on revenge and Shikamaru captured Hidan with his shadow and moved him off to fight one on one in a maze of wire and explosive notes. Hidan managed to free himself of the bind and swipe at Shikamaru, drawing blood. He started his jutsu and pierced his heart, Shikamaru wasn't injured though, revealing he had placed some of Kakuzu's blood on Hidan's pike. Hidan was surprised but continued to gloat. Shikamaru would not be shaken though. He would bind Hidan once again and sew the wire and explosive notes through his body. He then activated a trap on the ground, revealing a huge hole beneath the suspended Hidan.

Shikamaru let Hidan know he dug his own grave when he killed his sensei. He then lit a cigarette and flicked it at the notes, blowing Hidan to pieces. The chunks fell into the hole and Hidan yelled that he would get out, even as just a head he would bite Shikamaru to death. Shikamaru was unfazed and stated they were on his clan's land, and they would make sure Hidan stayed there undisturbed. He then collapased the hole walls down onto Hidan, effectively neutralizing him as a threat to anyone. Because of the drawbacks of the Kinjutsu used upon Hidan by Jashin, his inability to kill from his new home may prove to be his ultimate undoing.

Hidan was probably the most foul-mouthed, disrespectful character in the series; he frequently swore and complained at allies and opponents alike. He rarely used honorifics when speaking, and, even then, usually as a form of sarcasm. He was the only member of Akatsuki who did not respect their leader, Pain, and openly declared his willingness to kill him around others. The only respect he ever seemed to give was to his god, and, even then, he was quite willing to use his name as an insult. He openly held his partner, Kakuzu, in contempt for his habit of blasphemy, love of money, and Kakuzu's frequent ridicule of Hidan's religion and battle style. Despite this, whenever Hidan was in the mood to kill, the two worked together flawlessly in battle, and one can infer that he did care somewhat for his partner, from his panicked reaction when he almost killed Kakuzu while being possessed by Shikamaru's technique.
Hidan had absolutely no moral restraints regarding the people he killed; he considered slaughter a religious calling, and often took considerable pleasure in making his opponents' deaths as painful as possible. Given the requirements of his voodoo-like curse ritual, he was quite willing to inflict pain and injuries on himself, and openly relished the shared pain between him and the cursed victim. Despite this, he reacted "normally" (that is, he didn't enjoy the pain) to being injured by someone else, or when the opponent didn't share the pain.
Hidan was shown to be a sadomasochist, particularly during his ceremony, taking sincere pleasure in the pain he caused his victims and himself. His behavior in the anime bordered on insanity; he was frequently heard shrieking loudly while attacking, and laughed maniacally when he was about to kill Asuma Sarutobi. Hidan also appeared to be quite spiteful towards his enemies (and nearly everyone else), even commenting to Shikamaru Nara that "I've been waiting for this" ("this" referring to using his ceremony to kill Shikamaru).
However, his immortality had made him arrogant (though not quite stupid), and he frequently engaged opponents with no regard for strategy, save to acquire some of their blood. Although ridiculed for his foolishness by Kakuzu and Shikamaru alike, and being obviously inferior in tactical genius to either of them, he was able to analyze the nature and limits of Shikamaru's Shadow Imitation Technique, and conducted battle accordingly (though he retained his arrogant attitude even under these circumstances). Interestingly, he seemed to panic when Shikamaru took control of his body, shouting at Kakuzu to do something in a rather frantic voice. He didn't particularly like it when Kakuzu assisted in his battles, and only called for his help when he decided he needed it. Kakuzu tended to return the favor by coming in "late" and letting Hidan be beheaded (though still alive) as punishment for underestimating his opponents. After his head was reattached he showed a great hatred towards Asuma.

This technique is Hidan's primary method of killing his opponents in a way of the Jashin religion.

First, Hidan makes every effort to draw blood from his opponent and consume it. After that, his skin turns black with white markings representing a skeleton, a symbol of absolute death. He then draws Jashin's symbol on the ground in blood and stands in the center. This serves as the link between him and his victim.

Once his sacrificial ritual takes place, the victim is linked with Hidan until he either steps or is forced out of the circle. Any kind of injury that Hidan inflicts upon himself (or the injury they inflicted on him) is inflicted upon his sacrifice, be it a mere scratch or a pierce in the heart. If Hidan is forced to step out of the circle, the link is broken and the victim is set free, but all Hidan has to do is to step back into the circle to reactivate the link. Basically, this technique makes Hidan a living voodoo doll.

Hidan's immortality is due to the "successful experiment of the Jashin religion's secret jutsu", so he can fatally torture his opponents in any way he desires without killing himself, and he clearly enjoys the pain on himself as well.