We are buying an old house in Japan, and want to bring the bathroom into the modern era. There is currently only one old bathroom in the house, which is very dis-connected; great for multiple users at the same time, I guess - and that isn't a bad thing, but it doesn't feel like a bathroom. The design challenges are these:

1. Walls indicated with a triangle, and posts that are circled, are structural and cannon be moved (numbers in red can be ignored). I'm struggling to fit everything around these obstacles.

2. We would like to move the back door into the kitchen, which would also give us extra space for this project. However, this is a cost vs benefit decision, so we'll only do it if it offers reasonable benefits to the design.

3. Removing some of the windows would be fine. But, we would like to keep the large window beside the bath, as it offers pretty nice views across the valley.

4. We are also playing with the idea of having a door from the bathroom to the outside and having an additional outdoor tub and shower. But this is perhaps a little fanciful, and not essential.

5. We are thinking we will make the downstairs bedroom into a guest room for the time being and think it would be good to attach this bathroom to that bedroom as a private suite. This bedroom/bathroom will then function as our master suite when the kids get older and need more space on the second floor, so it would also need closet space.

6. If we make this a guest/future-master suite, we would need a separate powder room downstairs (or have the toilet separate from the bathroom to allow it to function for both), and a new family bathroom upstairs. The second floor bathroom will be used by the whole family now; only the kids as the family grows and we take the first floor master suite; and in the more distant future when the kids leave home, by guests.

The First Floor guest/future-master suite

Space for second floor family bathroom.

Guest Bedroom

Current bath/shower

Backdoor

Sink

Toilets

Second floor space for family bathroom

If you could suggest a layout that would work for this space, and meet our needs, we would be super appreciative! Thank you in advance.