Jiwon: I have studied Japanese for a few years now, though I have been way lax in Kanji x.x Can hold a conversation but I'm near illiterate. As for your question, this RP won't be set on Japan as much as in an original setting with Japanese themes. Like how many fantasy novels are not set in Europe, but the characters, themes, locales and such are obviously referent to it. So we got more leeway on ages and the like, just liked 18 years old as it seems like a good age. There may be some blackpowder present, but it will be incredibly rare. I won't say it doesn't exist, but barely anyone knows of it. 

Valerine: Very good pitch, you got to the meat of what I want in one. I got a very clear feeling for the character you'd make of the heir. Later on, if we go Sakuya, I'll start revealing more information about the setting, ask a few questions and the like to build up his sheet.