We have plenty of European pilots and they commute each month. So, yes, it's doable. I don't know what feedback you'd expect. 12 hours in an aircraft is very personal. It sounds like you think that's a lot but I wish I had a single sector 12hr flight. AJX pilots are subject to the same jetlag as other humans so we're going to be just as knackered as you think you will be. There's no getting round that I'm afraid and, yes, you do spend quite a few days getting over it when you get home and when you arrive back in Japan.
Some have single flights, others two and many have > 12hrs.
You 'make' time when going home. You 'lose' when going to work.
Long commutes are a pain and a waste of our lives. Don't apply for a commuting contract if you don't want to commute 12 hours.