1. Possibly in June. You may see better fares in the next month or so.

We were flying to Japan every year until our 2020 trip (via Chengdu) was cancelled. Generally we went Easter (we are bound to school holidays) and booked in October/November. Price of flights would range from £350 to £500. We have accepted that this era of low fares is probably over, we see it as unlikely to change this year.
We’ve always avoided travelling to Tokyo in the summer, lots of reasons for this (if you do go in June you’ll get a good taste of how oppressive it can be in the warmer months) but a big one is because that is when the cost of flights is at its highest. Since there is currently no difference between the price of flights in Easter or in late July/August we are now planning to have our daughter experience a Japanese summer. We expect our flights to come to about £900 each, but this is peak time. We rather enjoy stopovers, but it depends on where and for how long.

Some of the reasons you aren’t seeing cheaper fares is because the Chinese Airlines aren’t part of your options, neither is Aeroflot, and European airlines have longer and more expensive journeys to Japan as Russian Aerospace is blocked out.

My advice is to hold off for a couple of weeks (be warned that it could go either way after - or before - that) and be creatively minded with long stopovers.
Personally, I’m considering Bhutan, never had that as an option before. If there was a sub grand summer fare with a long stopover in Taiwan I’d jump on it. I will make my own decision in the next couple of months. I imagine June will have slightly more economical options.