A Demon Falling From Heaven?

You're a poor girl, who lives with your little brother named, Lukas. For short you call him Luke. A boy named Ciel tries to save you from the darkness, which he thinks is the cause that kills your little brother. He does everything to make you happy again, which he succeeds at. But, later on you turn a little evil. As, a 'man' named Claude comes for your delicious soul. The other 'man' named Sabastian tries not to take yours, he notices on how strong it gets, making him lose control. All he wants is to protect you, because you're the only thing that makes his master named, Ciel Happy. The thing is you also make Claude's master, Alois happy. Who needs you the most?