I was always taught in class when speaking to others to refer to, say, my hypothetical older brother as “ani” (mother as haha, etc) and other peoples older brothers as “oniisan” (mother as okaasan etc). I’ve been brushing up on Japanese recently, and have come across many native speakers who say that “ani” sounds distant and detached, and they’d refer to their own family as “oniisan” (okaasan etc). Is this a young person thing? Is the language moving in such away to phase out the formal/informal distinction in this case? Does the social status of who you’re talking to matter when deciding?
I know asking about Japanese honorifics is really opening up a can of worms, but I’m curious now.
In formal or semi-formal settings, you use “ani” to refer to your own, and a third party’s older brother and “onii-san” for the older brother of the person you are talking to. The same rule follows for all other family members.
Almost universally nowadays, in very informal contexts and when addressing family members directly, Japanese speakers will use the -san form.
This is not a new trend. In Japanese, surprisingly, adding honorifics can sometimes lower the level of speech. For instance, when talking to young kids, you will refer to cats and dogs as “neko-san” and “inu-san”.
I agree with you for older family members, but not for your imouto, musuko, tsuma, etc. I don’t think you would call them -san whether talking to them or talking about them.