Uhm, i'm not the author of the story, i'm just edit it after someone translate the original story from Chinese to VietNamese ( but it's too hard for everybody to read) so the main character is a Chinese girl ^^. And wwhy the girl can comeback to 30s of Germany ? It's because this type of fiction very popular in China and VietNam, back to the past or come to future by a mystery power (!?). I also don't know why the author want Chinese and German be a couple too, I decide to edit it because i like the background and the male characters. Sorry if the story uncomfortable for you :(. Uhm and sorry that I can't answer you sooner and for my bad English ^_^.
Hope this will help you. Danke
P/s: But you can understand Vietnamese ? I've never thought that i'll have foreigner reader. And glad to know that you are German because im very interesting in Deutsch and trying to learn the basic from internet now