So here's a question for people more familiar with japanese culture, why does Hinata refer to Kai as Kai-kun? Hinata pretty clearly hates Kai and Kai definitely hates him. Isn't Kai-kun way too familiar of an address? My understanding is that first name plus kun would generally indicate that you're on really friendly terms with someone.
Maybe they were friends in the past, but like how pathetic would you have to be to continue to refer to someone in a friendly manner even as they turn your life into hell. I just quickly skimmed through the early chapters and they are very clearly NOT friends. Hinata's at best a victim of Kai's bullying turned into a grunt.
It's hard to understand, since this doesn’t exist in English. But understand that "kun" is not a
"cute" way of addressing someone. Rather, it’s more like an
informal way of saying "mister" (note: it’s not
exactly an informal way of saying "mister", but that gives you the idea). In Japanese, they use "kun" more with friends and classmates. And you don't necessarily need to be friends with a classmate to call them "kun". Just being classmates,
even if you don’t get along, you can still use "kun" with them. Because again, "kun" is not an expression of
affection, but rather an informal way of addressing a fellow classmate as "mister".
The Japanese also share a bit of that Korean-like culture regarding age. So if you know someone is older than you, it’s common to use "san" with them, and the older person would call the younger one "kun". In other words, in a company, you would call a senior employee "san", and that senior employee would call you "kun".
Now, in the case of "chan", it’s a little different. Like "kun", it's also an informal way of saying "miss". But unlike "kun", "chan" is also used in a more affectionate way. However, among girls, it works similarly to "kun", if one girl is a classmate of another girl, it’s acceptable to use "chan", even if they aren’t close friends. But for a boy to call a girl "chan" without a certain level of friendship is seen as pretty disrespectful. That’s why boys usually call girls "san", even if they’re classmates, unless they know each other well. However, "chan" is also used affectionately when referring to children, pets, and in other similar situations. And although I said that "chan" would be an informal way of saying "miss", understand that this was just to help you grasp the idea. In reality, "chan" can be used for both boys and girls when they are children. In fact, although it’s rare, it can even be used for adult men in certain situations—but usually in a teasing or playful way.