If interested in this promotional deal with Turkish Airlines please look for flights in travel period till 26th of June 2015. Valid for bookings made till 28th of February 2015. If you need to book your accommodation in Japan you may compare hotel rooms offered by various leading booking sites through this tool.
Booking samples
Switzerland - Tokyo for €426 (CHF450) - direclty with Turkish Airlines
Switzerland - Tokyo from €393
Switzerland - Osaka from €406
Vienna - Tokyo/Osaka from €426
Germany - Tokyo/Osaka from €466
UK - Tokyo from Ł393
Geneva - Tokyo - London for Ł316
Flights have one layover in Istanbul on both outbound and return flights to/from Asia. Turkish Airlines allows to book stop-over there for slightly higher fare. All the European cities are weill collected by many low-cost carrier. The easiest way how to compare your connection flights is thorugh Skyscanner.
Booking sample of cheap return flights to Japan from Europe for €393 here. In this case you would be departing from Geneva to Tokyo on 10th of May. Return flight from Japan back to Europe would take place on 23rd of May 2015.