1. Set in an alternate universe, something similar to Game of Thrones (you don't have to have read the books or watched the show). A king is old and ailing. He has a son ready to ascend to the throne and a daughter that is a few years younger (or we could have a larger age difference between the siblings). The brother and sister have always been close, closer than most siblings are or perhaps should be. As they've gotten older things have changed, including hormones and emotions. As their father urges his son to find a husband for her (particularly one that will benefit their kingdom), the brother finds that the more he thinks on it, the more he can't stand the idea of any other man's hands on her but his. (The sister would obviously return the feelings.)
2. Set in modern time, a young, single father finds himself struggling with his teenage daughter. He met her mother, a woman older than him, when she was in the early stages of her pregnancy and fell head over heels for her. They got married and when the baby girl was born he claimed her as his and gave her his last name. When she was five things changed and her mother, feeling smothered, decided that family life was no longer for her. After she left her father threw himself into raising his daughter and being there for her. As she got older she began to take on household tasks that her mother might have been in charge of such as laundry, cooking, some cleaning, and she took a part-time job the second she was able to help pay for some of her own things instead of burdening her father. This meant that their relationship was more of an odd combination of parent/child and a partnership. At 17 she is hitting her rebellious stage late. It doesn't help that she's having steamy dreams at night and during the day of her father, ones she know she shouldn't but can't help. Making him angry at her seems like an easier solution than risking giving in to her urges when he's too nice or affectionate. (The father would obviously return the feelings.)
I'm a fan of angst and drama. Both are open to discussion and questions.