This one is long, but very important. Please read on the historical fiction cover type too :3 That one is also very important-- it goes not only for that genre, but all genres. This also includes the idea of inserting foreign country settings-- like Japan, into your manga. You want to be sure of thinking where your character will be set in, just draw and write about the most you know and make sure any information such as culture is correct. Research and even visiting the countries themselves, are important. You don't want people offended because you write about what you don't really know.