Disclaimer: I own nothing.
Kakuzu figured he wasn't quite the youngest anymore when the Akatsuki got a few technical devices; he just couldn't seem to become friends with those. What happened to good old communication jutsu? Carrier pigeons? Smoke signals?
When he first saw Konan without her cloak, he (unlike the rest of Akatsuki) didn't find her 'hot'; his first words were "Put some proper clothes on, young lady", and God, did he want to smack himself for that.
Okay, he was old, but he wasn't old old, right? He was still as athletic as ever, he barely had any wrinkles, and surely he didn't have a dachshund.
It was a slight comfort to his ego when he got himself a young lover in Hidan. Hidan, with only 22 years, was still much like a teenager in certain aspects – meaning he was horny as hell and reacted to even a slight brush of Kakuzu's hand to his crotch.
Kakuzu wasn't; he had control over himself. Despite Hidan's complaints to get viagra, Kakuzu was convinced it didn't mean he was old, just that he was experienced.
"Ah, fuck, Kakuzu – Kuzu – ahh, harder! Fuck me against the wall!"
"Oi, Hidan, stop fidgeting, you're heavy."
"Unnngh, I'm gonna – I'm gonna -"
It was generally no secret in the Akatsuki that Kakuzu and Hidan were fucking – mainly because Hidan was loud. When the two had sex, the entire Akatsuki base knew.
That time, though, everything quieted down before Hidan's infamous orgasm sounds.
Everyone looked up from the TV when the door to their shared room opened and Hidan emerged, face flush, clothes in disarray and expression a mix of embarrassment and sulking. "Um. We kinda need a fucking medic nin, seriously."
Pain narrowed his eyes in suspicion. "Where's Kakuzu?"
"...Did you kill one of his hearts again?"
"It's not my fault!", Hidan burst out. "He's a fucking old man, if he can't do certain positions anymore, he should've fucking told me, seriously!"
"What the hell is wrong with Kakuzu? I'm not getting a medic nin until you tell us."
Hidan blushed, looking down at the ground and sulking. "Ah, y'see, so, he was pretty much fucking me into the wall, the whole kinky 'my legs wrapped around his hips' thing cause he can go really fucking deep then, and his back just kind of... cracked?"
Hidan coughed, crossing his arms over his chest. "Kakuzu had a lumbago."
Hidan mentally counted down from ten, and punctually on "one", everyone burst out laughing.
"That's what he gets for being a fucking cradlerobber," Kisame gasped between laughs.
Hidan's face turned bright right. "Hey, I'm not fucking underage!"
"Yeah, but when you were, he was what, over eighty? It's just not morally right for him to be fucking with you."
"...Since when do we have morals, Kisame, we're the fucking Akatsuki."
"Will someone already get him a fucking medic nin?!"
It was way funnier in my head. Perhaps it would be better as a comic -.-