And am wondering if other readers actually understand what happened in the end, what with the talk of REGISTRATION.
Mako and Ito registered THEIR MARRIAGE.
At the age of nineteen.
Unlike in Western countries, where the registration of a marriage takes place at the ceremony or after, in Japan, you have to register your marriage before you can arrange for the wedding ceremony. All it requires is that the couple sign some papers, so even young couples can do it without worrying about planning the ceremony for the time being. Sometimes, I think, people manage to arrange for the two (registration and ceremony) to be on the same day...but this is rather uncommon. Well, most people are sleeping together before they register anyway, so it hardly makes a difference in that department.
But yeah, I'm quite glad I finished this series after living in Japan, so that I actually understand what they did (and also how easy it was for them to do). It's a big thing...but also not, in a way.