1. In Osaka we can wear jeans and the weather is likely to be "jeans and jumper" kind of weather
2. In Tokyo we're tourists so we can do whatever, but it might be a bit colder than Osaka.
3. In Kinomoto (the village near Biwako) you'll need that same jeans and jumper but with thermals and a jacket standing by!
4. Two of the three churches we're visiting are a little more formal, so slightly better than jeans and jumpers would be appropriate there.