There’s not a detailed dress code, but we are expected to dress at least semi-formally: slacks, shirt and tie for men; slacks, skirt, or dress for women. Japan has this thing about shoes, as in you often have to change them to “indoor” shoes, depending on the location. A lot of people end up with incongruous footwear for indoors. Many of my co-workers wear sneakers or sandals with their suits. I bought decent semi-formal shoes so that I don’t look like a peasant playing dress up.
I wear a full suit on days when I have to interact with the public. I wear slacks or dress pants and a button-up shirt with a collar every day, and almost always wear a tie also. I often wear a sport coat or similar jacket, except in summer.
Summers in Japan are brutally hot and humid. Some places don’t use air conditioning except on the hottest days, and those that do use it will often have it set between 26ºC and 28ºC (78ºF—82ºF) per energy-saving recommendations. They sell “summer suits” here, but frankly they almost always look shitty. They aren’t seersucker or linen or good summer-weight wool, like you see for formal wear in the South and the Caribbean. They just look cheap most of the time.
I actually dress better than we’re tacitly required to, most of the time. Even when I’m “dressed down” compared to my co-workers, I tend to pick classic styles instead of trendy things, and quality over quantity, so I often look better (at least I think so) in slacks and a sport coat than they do in their cheap “fashionable” suits that will look dated in a year or two. My thinking is, if you’re going to do it, do it right. If you’re going to dress up, buy good stuff that will still look great in 10–20 years.
Of course, my comfort clothes — what I change into when I get home and hang up my nice things — are jeans, khakis or 6 pocket pants; t-shirts (usually plain); casual button-up shirts; and, as cold as it is right now, a nice wool sweater. But even on my (rare) days off, I tend to dress far less casually than I did when I was in my 20s. Part of that is due to maturity, being accustomed to more formal styles, and part of is is that I can actually afford to dress well.
Thirty-dollar jeans and a $20 shirt used to be “dressed up” since I couldn’t afford a suit that cost hundreds of dollars, even if a good suit would last for years. Now, I can buy that suit, and since I can afford it, I buy better quality things that last longer even if I am buying casual clothes.