Tsukumihara diaries is a fiction based around the one world concept and development of the characters through short stories. The basic premise is that all of the Tsukihime, fate stay night and fate extra (as well as the expanded universe of fan and original characters) are present in a single world and further in the same city, the characters remain the same for the most part save that because characters like Shiki and shirougo to the same school they would be aware of each other. Adult stuff can occur in the story but the major three three rules are as follows.
1) characters cannot be majorly represented by their relationship with their partner
2) before a character can be romantically involved with others a minimum amount of time in the story needs to pass
3) while the intention is that you the readers have input on story development and while I'm notsuch a hopeless romantic as to think every relationship ends happily if two characters get together in a relationship please avoid suggesting their break up for no reason, and no, because I don't like it is not a reason.
finally I'll answer any questions and remember to have fun with this, I know nasu and fen write downers but I'd prefer the story be more bright UPS then terrible downs.