Hidan was one of the most foul-mouthed, disrespectful characters in the series; he frequently swore and complained at allies and opponents alike, contrary to being a "religious" person. He rarely used honorifics when speaking, and, even then, usually as a form of sarcasm, for example when he called Deidara "Deidara-chan". 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's 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, 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.
Abilities
Hidan standing within the Jashin symbol preparing for his ritual.
Immortality
Hidan's primary ability was his inability to die, a result of extensive experimenting with the Jashin religion's various jutsu. His immortality allowed him to survive numerous fatal injuries, and almost any form of dismemberment; he even retained his ability to speak after having his head cut off.However, his head still needed to be connected to his body in order to control it, so Kakuzu reattached it, and other body parts, when needed.Despite Shikamaru's attempt to blow him into smithereens using hundreds of paper bombs adhered to his entire body, the former only succeeded in decapitating him (after weakening the tendons that Kakuzu used to re-attach his head) with the full impact of the explosion. Even though he was impervious to most physical attacks, as well as survive the injuries that actually got through to him, he was still susceptible to pain, which he came to find pleasure in at the expense of his opponents. This inability to die was the primary reason for his partnership with Kakuzu. Since Kakuzu couldn't kill him, Kakuzu didn't need to find new partners after his fits of rage.Although the two disliked working together, this advantage made them the ideal team. His immortality was exploited in mutual advantage by Kakuzu, where the pair would perform a combo involving one of Kakuzu's hearts using a wind release jutsu in unison with Hidan striking at an opponent. Such an attack would maim the victim but leave Hidan unimpaired. Despite being "immortal", he is still capable of dying from a lack of nutrients.