The Akatsuki from Naruto: Shippuden make up probably one of the most iconic villain groups in all of anime. The aim of their organization was to capture all the Jinchuriki and Tailed Beasts. To achieve this more quickly, they divided themselves into two-man squads, each with their own targets. Each team had its own strengths, but one duo in particular stood out above the rest: Hidan and Kakuzu.
On paper, Hidan and Kakuzu have wildly different personalities and don't seem like they'd get along at all. Kakuzu is an irritable, calm and calculated fellow whose main concern is how much money he can make out of any situation. Hidan is a religious fanatic who aims to have as much fun as he can through indiscriminate slaughter in the name of Jashin. As one would imagine, Hidan constantly gets on Kakuzu's nerves, yet their relationship endures because of one key fact: Hidan can't kill Kakuzu.
Hidan's immortality makes him the perfect (or rather only) teammate for Kakuzu, given the latter killed everyone else he was paired with. It also plays a huge role in how they work so well together in Naruto: Shippuden. Both prefer to fight solo but are capable of deadly combos if they feel up to it. Hidan is a taijutsu specialist and while Kakuzu isn't too shabby himself, he excels in elemental jutsu. Their combo attack starts with Hidan engaging his opponent in hand-to-hand combat. Once they're fully immersed in the battle, Kakuzu blasts the pair with a widely-spanning jutsu. Hidan heals up just fine, but their attack spells almost certain death for anyone caught within it.
They also understood each other and frequently went out of their way to accommodate each other's requests. Kakuzu may not have understood Hidan's religion or anything about Jashin, but he always (reluctantly) watched over Hidan as he performed his rituals. Kakuzu returns the favor by escorting his teammate to pick the bounties he earned at various collection points. The duo makes a big show of complaining about how annoying the other's requests are, but from how they bicker and tease each other on their journeys, it's obvious they enjoy the company.
Their differing personalities also make them more enjoyable to watch than the other Akatsuki two-man cells. Hidan is quite boastful and loud, taking pleasure in verbally berating his opponents. When he starts on one of his rants, Kakuzu never fails to knock him down a peg in his usual measured manner. The teasing isn't one-sided either, as Hidan pokes fun at Kakuzu every time he does something uncharacteristically nice.
Hidan and Kakuzu have arguably the best and most effective working relationship of all the Akatsuki in Naruto: Shippuden. While the other cells are capable of teamwork to some extent, it's never with their level of finesse or cooperation -- and they certainly don't have Hidan and Kakuzu's camaraderie.
