Sorry for the late response, but the topic has finally been resolved. We got the rebooking that was offered by ANA at the very beginning. But as I told you, lesson learned as travelstart said "Hey, we offered you a rerouting (the strange iteration via Frankfurt and Osaka), if you don't like it, pay a service fee and we will ask the airline if you're requested rerouting is available." As the service fee was only 20€, we swallowed the pill and now the booking is valid again with the acceptable iteration.
But fun fact, if I check the booking at Eurowings it still says there's a valid booking for 12/25 at 12:25. That booking system is really slow or stupid...