Korean, Asiana and Vietnam Airlines can each do it from London for around £2.6k
Or ex-Eu:
2,550.08 GBP
Outbound - Sunday 25 October
07:45 Sun Brussels National (BRU)
08:00 Sun Heathrow (LHR), Terminal 5
British Airways British Airways BA389
Business Class
10:45 Sun Heathrow (LHR), Terminal 5
07:30 Mon Haneda (HND), Terminal I
British Airways British Airways BA007
Business Class
Inbound - Friday 30 October
10:50 Fri Haneda (HND), Terminal I
15:40 Fri Charles De Gaulle (CDG), Terminal 2E
Japan Airlines International Japan Airlines International JL045
Business Class
17h 53min
19:07 Fri Charles De Gaulle (CDG), Terminal TN
20:43 Fri Brussels Midi Station (ZYR)
Air France Air France AF7187
Business Class Operated by Sncf
(on this fare, you can only come back on the Thursday at c 11am...)