Naming conventions in Japan (modern and Kamakura eras)

[milkcho]

I am in the planning stages of a novel where the main character is a Canadian female living in Japan and married to a Japanese local, who's father was an American soldier stationed in Japan. I was told that Japanese couples have to choose one of the spouses' last name for the two of them, meaning that it does not necessarily have to be the husband's last name, correct? My female protagonist has chosen to take her husband's name for various reasons, but I wonder whether he would be more likely to have the surname of his Japanese mother or his American father.

I also have another story set during the late Kamakura shogunate, and I have had tremendous difficulty in finding any information about first names for non-samurai classes (my characters belong to artisan families). Would all social classes have the same kind of names or would there be restrictions for those who do not belong to the elite? I would also like to know about outcastes and whether someone forced to join an outcaste community (after being punished for committing a crime) would have to change his name for some reason. I've googled things like naming conventions and personal names in old Japan, and adding artisan class or outcastes, but the best I've gotten was very samurai-centric.

And just throwing this out there in case anyone can think of something: does anyone know of a Japanese mythological creature that can travel to the past or control time in some way (or an object or magic that could grant this ability)? I've read that some very old kitsune were thought to be able to bend time and/or space, but that's about it.

Thanks a lot in advance! Any bit of information would be very, very helpful.