Where did the "# years of pain" originate from?

Question

So when I first saw Naruto seeing the scene where Kikashi uses his "1000 Years of Pain" on Naruto when he tried to get everyone's lunches when Kakashi isn't looking i thought this was just some joke made up in Naruto.

the other day watching A Lull in the Sea in Episode 15 I Saw Hikari chasing Ikari's son doing the same thing saying "kanchou kanchou" and telling Ikari he was going to give him "3 years of Pain". i also seems to remember seeing Ikari's son do it do someone

Both Hikari and Kikashi do mostly the same thing, they clasp their hands together with their index finger pointed out and poke their target in the butt

Now i am wondering where this poking someone in the butt originate from? Is A Lull in the Sea getting it from Naruto or is it from something else in Japanese culture

Answer 1

It is actually a Japanese prank known as kancho.

From the Wikipedia article on Kancho.

Kanchō (カンチョー) is a Japanese prank performed by clasping the hands together in the shape of an imaginary gun and attempting to poke an unsuspecting victim's anus, often while exclaiming "Kan-CHO!".

The word is a slang adoption of the Japanese word for enema (浣腸 kanchō).

According to Naruto Wiki:

This technique's full name is "Konohagakure Hiden Secret Taijutsu Technique: One Thousand Years of Death" (木ノ葉隠れ秘伝体術奥義・千年殺し, Konohagakure Hiden Taijutsu Ōgi: Sennen Goroshi, Viz: Konohagakure's Most Secret and Sacred Technique: One Thousand Years of Death, English TV: Hidden Leaf Village Secret Finger Jutsu: One Thousand Years of Death, UK DVD: Secret Ninja Technique of the Hidden Leaf School, Death for 1000 Years, English Games "Sacred Taijutsu: 1000 Years of Death").

It is mentioned that Akira Shiotome (Miuna's brother) loves playing kancho:

He enjoys playing kancho with Hikari Sakishima and Shun Sayama and after Manaka awakens, the two enjoy playing with each other.

Also, in the scene where Akira played the prank in the 15th episode of Nagi no Asakura, he only said "Kancho". The person who subbed it in English probably wrote it as "# years of pain" as a tribute to Naruto.