I managed to nab a First class seat from Frankfurt to Haneda on Wednesday May 11th using Virgin airmiles.
When I tried to nab the Business seat back on Thursday 26th (the 00:10 flight from Haneda) it came back as UNCONFIRMED from ANA when Virgin tried to get it.
Same for Friday 27th.
So went for an Economy seat back and will keep checking.

Both days are showing as available on United, any reason the 00:10 Business seats might be ...... difficult to get stil??