KakuHidan

"Hidan: Hey, look at that, it's my headband! You went to the trouble of picking it up and keeping for me? I'm touched. You're a pretty nice guy, Kakuzu, you know that? Kakuzu: Shut up. Let's go. Hidan: Let me put it on at least! Okay, I'm coming. Admit it, you like me a little, doncha? Kakuzu: Either you shut up, or I'll kill you. Hidan: Haha, you're embarrassed! I understand."

- Naruto Shippuden #83

KakuHidan is the slash ship between Hidan and Kakuzu from the Naruto fandom.

Canon
Kakuzu and Hidan were both partners in the criminal organization Akatsuki, whose members were arranged in pairs. It is said that Kakuzu had previous partners, but he killed them all eventually due to his lack of patience. Hidan was the newest member of the Akatsuki before Tobi joined. Hidan was paired with Kakuzu because as he is immortal, it does not matter how many times Kakuzu loses his patience at him, he cannot be killed. Kakuzu is considered immortal too, being able to steal hearts from other people and keep them as backup in case his main one is destroyed. Because of this, people call his partnership "the zombie combo" (zonbi konbi) in Japanese. Kakuzu and Hidan are very different persons with almost opposing views of life and the world. Kakuzu has lived for nearly a century, having snatched healthy, younger hearts to extend his life. This has given him a kind of experience in life that makes him value personal belongings above everything else. Kakuzu is the Akatsuki treasurer, the one who manages earnings and expenses. He also goes out of the way during missions if a chance to improve his personal wealth arises. Hidan is a Jashinist. A follower of the god Jashin who has been granted immortality in exchange of blood sacrifices.

When they work together, they constantly bicker and complain about each other's actions and decisions. Kakuzu complains about Hidan's blood sacrifice rituals to Jashin being too long and pointless. Hidan complains about having to follow Kakuzu while he tracks down, kills targets from the bingo book and redeems his reward. He also complains about having to carry the dead bodies for Kakuzu instead of sacrificing them to Jashin.

Despite their differences and constant arguments, Kakuzu and Hidan are shown to care about each other. Kakuzu kept Hidan's forehead protector when he lost it during a fight and Hidan looked terrified when he found out that the blood he used for his ritual wasn't Shikamaru's but Kakuzu's; meaning that he had injured him instead.

In the Naruto novel "Akatsuki Hiden", there's a chapter where Hidan and Kakuzu are sent to a village which was built to shelter wanted ninjas from the bingo book. Their target is one of the criminals. They wander around looking for the town for several days but they can't find it. As they are in a remote place, Hidan starts worrying about Jashin punishing him if he doesn't bring Him sacrifices soon. He prays often, asking for forgiveness, while Kakuzu finds these prayers terribly tedious and time wasting. Hidan eventually sits on a stump and lets Kakuzu find the village. When the man they're after finally comes out, they argue about who will the one killing him. Hidan does it in the end, as Jashin still needs blood and Kakuzu waits for him sitting on the stump. After killing the man, a child appears and says Hidan's technique was cool. Kakuzu asks the kid where he came from, and he explains that there's a village nearby, he also says it's protected by a genjutsu and one needs to know how to enter. Even when the mission is done, Kakuzu can't miss the chance to hunt a few more wanted ninjas, and Hidan wants to keep sacrificing people to his God, so they follow the kid.

In one of the movies, Hidan believes Akatsuki is a music band and guesses that Kakuzu is "the bassist".

Fanon
One of the reasons people ship them is because they are work partners and enjoy their bickering dynamics while at the same time sill care about each other. As Hidan is canonically a masochist, bdsm themes are common in this ship. There's a Kakuhida Week held every year on October since 2018. AO3, there are currently 890+ written works.

Fandom

 * FAN FICTION

Trivia

 * After he gets temporarily revived using the Edo Tensei technique, the first thing Kakuzu says when he sees Shikamaru is asking about Hidan's fate after he died.