Depend on which restaurant where you go and it is always safe to check with the particular restaurant where you are going. In general, it's safer to be formal. Don't expose too much skin, no flip flops or sandals, no jeans and don't wear strong perfumes as kaiseki cuisines value aroma of the food as well.
When in the restaurant, talking with loud voices and getting too drunk are inappropriate as well.
It's nice to study about Japanese eating manners before you go.
I recommend to wear a jacket and a shirt. It may not needed to have tie for men, but in any case, it requires to wear formal clothes absolutely. It doesn't prefer exposing a lot of skin. You must not wear perfume, flip flops, sandals, jeans ...etc.