Are those things considered way more important than sexual compatibility then? What happens if they eventually have sex and one partner is severely disappointed, but they've already invested so much into the relationship?

> Are those things considered way more important than sexual compatibility then?

I wouldn't say "way more important", but I think people would rather have a partner who they fit well together with as a household, enjoy spending time with, raise children well together (or not, if that's what they're after) etc. and have mediocre sex than someone who they had great sex with but didn't have a great relationship outside the bedroom.

(If you want to be cynical you could say it's because Japanese culture puts less emphasis on sexual fidelity, particularly in the case of paid sex workers; while a lot of westerners overstate how common or normal it is, it's certainly not unknown to have a more-or-less happy marriage where one or both partners are having sex outside and this is known and accepted by the other)

> What happens if they eventually have sex and one partner is severely disappointed, but they've already invested so much into the relationship?

Either you decide you can live with that, or you can't and you break up, which is presumably the same thing that happens if Americans date for a while and then find out they have incompatible life plans. To me it be worse to get invested in your relationship with someone who you have great sex with and then you find out one of you wants kids and the other doesn't, or one of you wants a high-income lifestyle and the other doesn't want the stress, or you never find the same things funny, or...

(I wouldn't say it's a huge investment - we're talking a few months of dating and going exclusive with that person. But you've got to put in a bit of sincerity)