Dress code for most restaurants in Tokyo/Osaka/Kyoto?
If you cannot find anything about a dress code there probably is not one. Sushi and tempura have traditionally been "fast foods," food as likely eaten during the Edo era at street stalls as in restaurants. Jeans are fine, as is a suit and tie. Customers are probably dining after work, so their attire is more likely to reflect their work clothes than what the restaurant expects. Remember, most For Italian food you may ant to dress up a bit more, if you feel more comfortable. Come to think of it, I cannot recall ever going to a place with a dress code in Japan. Have others?
I never saw a formally posted dress code for anywhere but the restaurants in the Park Hyatt and it's fairly relaxed (no flip flops or sports gear, and no dress shorts after 5PM) but it's not exactly Japanese is it?
In my recent 3 weeks in Japan including several Michelin starred establishments I never felt uncomfortable in dark jeans or black cotton slacks, a dress shirt and sometimes a sport coat, never took the necktie out of my bag.