In Yokomichi Yonosuke (A story of Yonosuke) each time Yonosuke introduces himself other people seem to be amused by his name. Why is that? Is this some kind of Japanese wordplay?
As it was brought up in the chat over at japanese.stackexchange, here's my take on it from a language perspective. I haven't watched the movie.
The Japanese spelling of his name is 横道(yokomichi) 世之介(yonosuke). Note that in Japanese the surname comes first.
Here's an interview with the writer Shuuichi Yoshida (吉田修一) I found.※
I decided I wanted to write a story about an 18 years old teenager who comes to Tokyo to start his life as a student at an university. I thought I would name it after the protagonist. I came up with the name Yonosuke first, and had been thinking what to make of his surname, when the mistress of the pub where I went regularly suggested "Make it rhyme." Together with the other customers we started to scribble many surnames beginning with "yo" on our beverage coasters: Yoshida, Yoshio... we came up with many candidates. As the name Yokomichi came up, everybody was like "Ah!" and we all agreed on this name unanimously. So it was decided. I'm from the Nagasaki prefecture, and there we've got a word "Yokomichi-mono" (横道もの) that refers to somebody who's a bit lazy or is slacking off, and there's also the expression "Yokomichi ni soreru" (lit. stray off to a side road; stray away from the topic) .., that's the kind of nuance behind his name.
His surname, Yokomichi is a normal Japanese word and literally means "side road". It's not exactly a common surname, and it's like if you introduced yourself as
I'm Mr. Sideroad. It sounds like somebody from a more rural area as well.
Often you might introduce yourself with your surname only, but imagine you add his given name Yonosuke as well. It sounds a bit funny just by virtue of rhyming (alliteration) with his surname.
介 (suke) derives from the name for a governmental official's rank; and quite commonly used for male given names, and doesn't really mean anything anymore and is more like a staple name. 世 (Yo) is "world, epoch, current times". Suke might also be a pun on 助 (suke), "support, help".
"John Smith" is an English staple name, and to illustrate, Yonosuke would be a bit like
John (of the) World.
※ For reference the relevant part of the interview in the original Japanese.
Sounds like it's the sort of name you'd expect to hear on a country bumpkin... like Cletus in the US, maybe (sorry to anyone named Cletus who may be on SE).
Much of the charm of THE STORY OF YONOSUKE inevitably rests on the character at the centre of the film. Although it may not be evident to outsiders, the very name Yonosuke Yokomichi has a peculiar resonance in Japanese that amuses everyone who meets him. It’s a joke name, the name a comedian would have, a name that could only come from rural Japan and sound ridiculous to the more sophisticated young people of Tokyo.