I love reading fanfics, but sometimes fanfic writers can be pretty ignorant when it comes to using Japanese language, or embedding Japanese culture into their fics. Which I totally understand, because most of them are probably not Japanese, neither am I. I've only been to Japan several times and the longest time I stayed there was 6 months. And that doesn't make me an expert in Japanese language nor culture (far from it^^;). However, I'd like to share what I know and hopefully what I wrote here is mostly correct ^^; If anybody finds an error or has any questions, please don't hesitate to tell me. m(_)m

• First of all, the weiß cast obviously don't look Japanese at all. But then again, it's anime. You can do anything in anime, including defying the basic laws of nature, making Japanese the language of the world, and creating overly beautiful male characters. heheh.
• However, the setting of the story is still Japan. And the cultural boundaries still apply.
• And so, it kinda disturbs me when in a fanfic, an original character is introduced with a non-Japanese name but treated as if he/she is a native Japanese/whatever country the writer wants the place to be. Japan is not as diverse as America, so when I see a non-Japanese name, I automatically assume he/she is a gaijin (foreigner).
• But a made-up Japanese name that doesn't sound quite Japanese is kinda weird too...
• Aya/Ran calls his sister 'Aya' with no '-chan'. And Aya-chan calls Ran 'Ran-nii' in the manga. I'm not sure how she calls him the anime though. Gotta watch the series again. However, I doubt that Ran actually calls Aya-chan 'imouto' or 'imouto-chan' as some fanfic writers like to use. In Japan, people call their younger siblings by their first names. I have never heard somebody calls his/her younger sister 'imouto'. That just sounds weird. There are special terms for older siblings, but there's none for younger sibling (info courtesy of Cat)
• More about suffixes.. I think only Omi calls everybody by their first name plus '-kun'.
• Youji, Ken, and Aya use male speech. They say 'ore' for 'I'. Omi uses more boyish speech. He says 'boku' instead of 'ore'. I think Crawford uses 'watashi' because he uses polite language, but I'm not sure.
• I see some fanfics used the word 'yamete' (some people even mispelled it), and it was the guys who use it. Actually for guys, they use the more masculine form 'yamero' or 'yose' depending on the context. Making them say 'yamete' makes them sound girlish ^^; Boys are exception though. Omi uses boy speech, so it doesn't sound weird when he says it^^
• More to be added if my brain can think straight...